- Email: [email protected]
Notes on meteorology
O~tob~r,~9o5]
Notes on Meteorology
NOTES
31
ON METEOROLOGY.
Br W. H. SYMONS, M.D., D.P.H., Medical Officerof Health and City Meteorologistfor Ba~h. METEOROLOGYand meteorological instruments have always interested me ; and in the following notes I have endeavoured to bring together some points which I think may interest you. I shall assume that you are all observers, and acquainted with the forms of meteorological instruments and methods of using, as described in that excellen~ little book, Hints to Meteorological Observers, by W. Marriott, published by Edward Stanford for the Royal Meteorological Society, and, therefore, I may at once proceed with my remarks. Choice o/ a site ]or a Meteorological Station.--As a rule there is very little choice. The site has to be where continuity of observation is probable, and therefore usually in the ground of some public institution, except where the services of a paid observer are retained. Hence, it follows, many stations are badly placed. Many of the old records of rainfall are of little value, because the gauges were placed in most unsuitable positions. In giving evidence on behalf of the Bath Water Works, the late G. J. Symons stated that a correction of something 5ke 30 per cent would have to be made in forming any estimate from some of the records kept around Bath. Some of the earliest reliable readings, taken continuously for several years in this City, were the observations made by the first Medical Officer of Health, Dr. C. S. Barter, the rainfall from 1855 to 1868 being recorded in the first published annual report. His gauge was situated on the roof of his house in the Paragon. Fortunately, Dr. Barfer's records overlap those taken at the Royal Literary and Scientific Institution, and for two years did not differ materially. The latter station can hardly be considered ideal ; to keep the gauge away from children it was placed on the thermometer screen; the reservoir for rain water being in the screen, it is possible that the thermometric readings may be influenced by the temperature of the water contained in the reservoir. On the Continent it is customary to place the rain gauges five feet above ground; in England they should be one foot. Those placed five or ten feet above ground are said to collect about five per cent less rain than those placed on the ground, the wind carrying over the gauge. I have not found any regular difference between a gauge placed six feet and one placed one foot above ground. The Meteorological Society's Regulations require the rain gauge to be set in an open situatio~ away from trees, walls, and buildings, at
32
N o t e s on M e t e o r o l o g y
[P~biio IIealth
the very least as many feet away from their base as they are in height. My gauge at my old station was four times this distance from a wall, and yet I found that another gauge, placed twenty feet north of this, collected more rain when the rain was with u south wind. The sunshine recorder should be placed in such a position that the sun can shine upon the instrument the whole of the time it is above the horizon ; this is a condition very difficult to fulfil, as it must be also accessible for changing the curds. From north-east to northwest there must be no building or chimney more than 4° above the horizon, except due south, where u building 12° above the horizon will not obstruct. The recorder should be placed somewhere about the mean elevation of the district, the bright sunshine of which it is supposed to record. In Bath we suffer by having the recorder placed in the vu]ley, where the morning mists shut out some light. The four feet earth thermometer is another instrument not easy to place ; it ought to be where no shadow falls, and it must not be near any sewer. I had some difficulty in placing this instrument in the Institution gardens; the first spot I choose was a few feet south of the screen irt which the thermometers are kept, but I found it registered 9 ° above the temperature in my own garden : the waste water from the Hot Baths was carried off in a culvert a few feet away. Two other sites chosen were fomid to be influenced by sewers. It is also necessary to take into consideration the immediate subsoil, and to see that it is representative of the locality for which the return is made. But the earth thermometer need not be read precisely at 9 o'clock; an hour either side will make no perceptible difference; u record taken once a week is a useful record, when a daily visit to u suitable spot cannot be arranged for. The daily variation seldom exceeds half u degree, nor the weekly variation one and a half degrees Fahrenheit, ut four feet below the surface. Any thermometer which can be read to half u degree may be used us an earth thermometer, but I prefer to have them graduated like clinical thermometers to 0"2°; they can then be easily read to 0"1. They should have ]urge bulbs, and the bulb be embedded in some non-conducting material, such us paraffin. Messrs. Negretti und Zumbru make an earth thermometer which is very generally used. I t is completely encased in u glass tube protected b y rubber rings. The contaiuing iron tube, which is sunk in the ground, has to be wider than usual) but one seems to be able to take u good many liberties with the instrument used to measure temperatures at four feet below the surface. Using a one inch iron tube, I found that when the portion above the ground was heated to the temperature of boiling water for an hour or more, there was very little change of temperature at u depth of four feet---only a fraction of
October, 1905]
Notes on Meteorology
33
a degree--but at a depth of one foot below the sudace, changes in the temperature of the air distinctly agect the record. Therefore, I prefer to use a tube of non-conducting material, such as a glass tube. The tube should be closed at its lower end, and contain sufl3cient mercury to cover the bulb of the thermometer. A large glass tube is apt to be broken by expansion and contraction of the soil, and that portion above the surface must be protected by a metal tube. I have had one glass tube in use for several years, but it is only threefourths of an inch in diameter. The thermometer I use is an ordinary chemical thermometer graduated to one-fifth of a degree ; it is mounted in the case in which it was sold, the front part of the ease being cut away to expose the scale. No doubt a piece of bamboo cane would answer the same purpose as the case of the thermometer. Approximate records at one, two, and three feet may be obtained by suspending the four-feet thermometer in its own tube at these depths, allowing at least half-an hour for registering the temperature of each zone. For more correct readings the tube below the thermometer shoutd be plugged by a wooden plug, or, if for permanent records, by being filled wath earth or sand below the thermometer, to prevent currents of air influencing the temperature. For some months past I have taken daily readings of earth thermometers placed side by side: one a standard chemical therm.ometer, No. 12,209, in glass tube ; another hung in a thin copper tube, six inches proiecting above the surface; and another in a thick iron tube, twelve inches projecting above the surface ; a fourth similar to the standard, also mounted in a glass tube, but placed in a sandy soil, on the same plot of ground. The thermometers mounted in glass tubes showed that the temperature of the earth was failing at 1 p.m. ; the others would lead one to think it was rising ; the air temperature had risen 20 ° between 9 and 1 o'clock. Considerable alterations have been made at my own station, in that I have been able to secure a piece of land projecting 100 feet beyond the general line of gardens. The Stevenson's screen is freely exposed on the south and east, and 200 feet from any building in other directions. The subsN1 is blue gas rock about one foot below the surface of grass. At the Henrietta Park station we have one foot of soil upon sand and gravel, and the minimum on the grass is often considerably below that registered at Combe Park. I think this must be because there are no buildings within several hundred feet, and not because the soil is sandy. In m y own plot I have laid down a portion ten feet square with sand 18 inches deep directly on the rock, but with no soil or grass a b o v e ; t h e minimum thermometer, supported one inch above the surface of this sand, registers two or three degrees above the thermometer similarly exposed above grass; other thermometers 3
34
N o t e s on Meteorology
EXA~IPLE~ OF CLI~ATOLO(~ICAL STATIONS,
~r.bli. ~eslt~
Notes on Meteorology
October, 1~05]
35
upon asphalte and stone usually indicate intermediate temperatures, whale the thermometer placed on the screen and. one projecting from the screen, five feet six inches above the grass, show higher temperatures. The thermometer placed on the grass is very liable to be broken, and it would be an advantage if one could get the same information from a thermometer placed above the screen. The thermometer one foot below the surface in sand, registers three or four degrees below a similar thermometer in a loamy soil under grass in frosty weather. It is important to have 'one-foot earth thermolneters in glass and not in metal tubes, as otherwise the true temperature is not recorded. Fogs.--The density of fogs is n o t generally noted, and hence the records concerning fogs are almost meaningless. Nearly twenty years ago the !ate 5It. @. J. Symons wrote a strong plea for the establishment of fog gauges (Symons's Meteorological Magazine, xvii., 17), and suggested the erection of a slab painted alternately in white and black stripes~ the black stripes being ¼, ½, 1, 2, and 4 inches wide, separated by white stripes 6 inches wide; the black stripes to be numbered from one to five ; the amount of fog recorded to be that of the thinnest line which could be seen by an observer standing twenty feet in front of the scale. Such a meter may be suitable for the very opaque, small-grained London fog, the London particular as it is called, but for the coarse-grained fog one gets in the country, all the lines appear ahnost simultaneously as one approaches the scale, and I have not seen a fog in Bath when one could not see the whole of the scale at twenty feet, and, therefore, we may assmne we never get Fog 1 of G. J. Symons's scale. SCALE Outlines of objects visible at-- just
12 m i l e s 6
s
'.:
[
FOR
ESTIMATING
FOGS. Degree Visibility. of Fog.
0bj eets for Combe Park Station.
. . . .
V. 12 m . ""[
:::
"1 Combe Down, i~ath~i~pton D o w ,
12 f u r l o n g s ... ""! B e e c h e n Cliff, T w e r t o n R o u n d Hill ...IV- l ~ m . 6 ..... D e s t r u c t o r C h i m n e y , T w e r ~ o n C h i m n e y s I V. -~m . 3 ,: ...... i Locksbrook Chapel Steeple ...... V. ~ m . 1000 feet or 400 paces! A g a r d e n w a l l . . . . . . . . . . . . iV.400p. 500 , 200 , T r e e s b y brook . . . . . . . . . . . . V.200p. 250
,,
i00
,,
Garden
\vall
0
IV. 6 m . F. 1 ..IV. 3 ~. F. 2
. . . . . . . . . . . .
V.100p. F
F. F. F. F. F. F.
3 4 5 6 7 8
i understand the Meteorological Council have recently considered the establishment of a workable scale for estimating fog. I do not know what scale was suggested, but for some years I have used a scale based upon the limit of visibility ; a note being made of the distance
36
Notes on Meteorology
re~bl~ e ~ l t h
of various objects from the point of observation, the degree of fog being inversely as the distance. If I can see the outline of a hill six miles distant, but nothing beyond, I record F.1; if three mites distant F.2, etc. For dense fogs, some object belonging to the Meteorological Station may be used in determining the limit of visibility; the character of the back-ground will influence the result ; a light-coloured object, such as the Stevemson's screen, disappears from view before a dark object, such as the cups of Robinson's anemometer, or the stand of black bulb thermometer. The densest fog in Bath last year was on November 15th, at 9 a.m. I could see the screen at 50 feet but not at 52 feet; the cups of a low-level anemometer were visible at 70 feet. The ¼ inch line on Mr. G. J. Symons's scale could be seen at 50 feet, the 4-inch line at 80 feet. This fog was registered as F.10. Visibility 50 paces = F.9 ; visibility 25 paces = F.10 ; visibility 12 paces - F.20 ; visibility 6 paces F.30 ; visibility 3 paces :: FA0. At night, street lamps are convenient units of measurement, if their distance is known in paces. Visibility in a dense fog is easily determined to a pace, but fogs are usually patchy, and dense fogs vary from minute to minute, and also in different directions. I record the greatest density; it may be fairly clear in the north towards Lansdown, while on the south over the valley we may have F.6. Sometimes, however, it is foggy at high levels and quite clear at low levels ; generally we get more fog in the suburbs of Bath than we do in the city. I should regard a fog in which I could not see a man at 50 paces, in the day time, as an extremely dense fog for Bath. There was only one such fog during the past year, but in a dense London fog we may be tmabte to see a mart at 5 paces; one of the advantages of living in London is said to be you can see what you breathe° During 1904 1 registered fog on 61 days at Combe Park, namely: 5 times F.1, 15 1~.2, 20 F.3, 10 F.4, 2 F.5, 3 F.6, 2 F.7, 3 F.8, and 1 F.10. Only on six days was it so foggy at 9 a.m. that I could not see the outline of trees or houses 1,000 feet away in the valley of the Bath Avon. Captain Carpenter, in his report to the Meteorological Council, says: " T h e r e is no evidence of any special connection between the frequency or intensity of fogs and geological conditions, nor does the locality of the commencement of fog depend upon geological formation." " No severe fog occurred with an air temperature above 40° F." My limited observations lead me to think geological and physiographical conditions have much to do with the formation of fog, but the fog may be fairly evenly distributed after formation. Broadly speaking, an air temperature below 40 ° , an earth or river temperature
October, 19o5]
Notes
on Meteorology
37
above 40°, a more or less stagnant atmosphere, and the presence of dust particles in the air, are the four principal conditions tending to produce fog. Dust.--The estimation and examination of dust is rather outside the rotltine work of meteorology, but is of much importance and interest, and regular observations of the amount of coarse dust which falls in our streets would be interesting; but possibly our rainfall records answer nearly as well. Hesse's tubes and Petrie's dishes are commonly used for collecting dust in rooms, but these appliances are not suitable for estimating dust coming from a destructor or from building operations. In investigating a nuisance of this kind, one Medical Officer of Health used wooden frames, one yard square and six inches deep, placed on American cloth; the amount of dust collected daily or weekly being noted, and its quality determined microscopically. I have tried this method for comparing the amount of dust which falls in the centre of the City, and in m y front and back gardens at Combe Park, but a shower of rain upsets the record. I have also a zinc tray, one yard square and two inches deep, which i have used for tNs purpose; this is also useful for collecting dew. A more accurate plan for dust is to draw a known quantity of air through a suitable filter. I have used the paper candles sold for Soxhlet's Fat Extractors, and also a Pasteur's porcelain filter for this purpose, but a glass tube plugged with sulphate of potassium crystals and powder is perhaps the best filter.* The air is drawn through the filter by means of a water pump, the volume being measured by a small gas meter; the pump and meter may be in the house, and the filter a hundred feet or more away, the air being drawn through a ¼ inch compo pipe laid under ground. Mter filtration the air may be examined for amount of CO~, etc. Such observations are made regularly in Paris, but, as far as I know, not in England. Some years ago I had three such stations working at various levels around Bath, but want of time and assistance made me drop the work. Local currents coming from chimneys upset my estimation of CO.2. Evaporation.--The official evaporation tank is six feet square and two feet deep. This should be sunk in the ground, with the top level with the blades of grass, and should be kept filled with water to within about three inches of the rim. I t is not an easy matter to measure accurately the level of the water, on account of the movement caused by wind. I prefer to take the reading from a graduated gauge tube, which is in communication with the tank ; it is quite easy to read the * Sulphate of potassium being a soluble sMt does no~ interfere with the subsequent microseopieM examination of the dust nor with the estimation of organic matter.
33
Notes on Meteorology
~p~bn~ ~ t ~
level in the tank to one-twentieth of an inch. The tube must be capable of being closed by a tap. The gauge tube may be several feet away from the tank, where the ground is low enough to allow the observer to stoop easily to bring his eye on a level with the graduation of the tube. It is convenient to have a pit six feet away from the tank. After observing the level the water in the tube may be blown back into the tank and the tap closed, to prevent fracture of the glass by frost. The loss by evaporation for 1903 was t8 inches. Ozone.--The determination of ozone is not now included by the Royal Meteorological Society in its scheme of ordinary observagons, because the test papers employed are frequently unreliable. Mr. G. J. Symons thought it was a pity these observations were given up. He had papers placed in various parts of London, and had them returned to him for examination once a month. He found that winds from the country coloured the paper ; the winds which had passed over the metropolis never did. It does not need a large town to deprive the air of this property. When the wind is westerly the paper at our eastern station is not coloured, and when the wind is easterly the paper at the east station is coloured much more than that at the west station, although the west station is 100 feet above the east station, i[ find that paper exposed on the dome of the Guildhall is less coloured than the low level paper. Papers should be wetted, and the colour estimated as soon after removing from the screen as possible; but papers from various stations should be compared simultaneously. In preparing ozone papers I use white blotting paper. The sheets are cut into quarter demy, washed with a 5 per cent solution of P.B. hydrochloric acid, and then rinsed with water until quite free from acid, then dried. The starch compound is prepared by heating 5 grams of arrowroot with 200 co. of water, and adding 1 grant of potassium iodide. Twenty co. of this mixture is spread on each quarter sheet of paper, on a glass plate, and the paper thrown on to a wire to dry; then cut into slips, made up in books, and wrapped in tinfoil. Such paper may be kept for many years. Wind Direction.--It may seem a very easy matter to determine the direction of the wind, but practically this is by no means easy as regards light winds. Eddies caused by buildings are very troublesome ; smoke from a tall chimney is perhaps the best guide ; smoke from the ordinary house chimney is a very poor guide; if we observe three or four chimneys close together, the smoke may have a different direction from each one. In order to get the true direction the chimney top or vane must be forty feet above the buildings. The Pressure Tube Anemometer shows how the force of the wind
0~tob~, ~90,5?
Notes
on Meteorology
39
varies from second to second. When travelling more than ten miles an hour, it appears to be thrown wavelike against obstacles; the pressure is not continuous. Change in the direction of ~he wind is proverbially common, and 9 a.m. records are of little value ; probably more information can be gained by studying barometric gradients; the true direction o~ the wind is shown in the daily weather charts in this way, and also its force. It is quite easy to make seif-reeording anemoscopes, but, as before stated, difficult to fix them in suitable places. Messrs. Lander and Smith, of Canterbury, are now introducing a sebes of cheap recording meteorological instruments, which should prove very usdul to Medical 0t~cers of Health in checking the returns which they receive from various sources. It is surprising how few persons can take twenty consecutive daily readings of any inst,'ument without maNng a mistake; usuMly with thermometric readi *,he mistake is one of 5 ° or 10°, and with the barometric readings h. inch; such errors are easily corrected by se!f-reeording instrmnents, which are perhaps not su~ciently sensitive to entirely replace the non-recording instruments. Sun Spots.--The terrific storms which go on in the photosphere do not appear to imquence terrestrial atmospheric conditions, except as regards magnetic storms. But magnetic storms may have some influence on living organisms. I have endeavoured to keep a record d large sun spots duiing the past year, but fortunately it is easy to obtain early in March an accurate record of the position and magnitude of each group of sun spots for each day of the preceding year in the Greenwich Photo-Hdiog~aphic Results. Dm C. H. CAYLEY, one of the Divisional Health Officers of Bombay, some little time ago hurt one of his fingers, tetanus developed, and he died after a few days' illness. Dr. Cayley went out several years ago for plague work, but was subsequently elected by the Bombay Municipality as one of its Health Officers. DEATh OF DR. T. It. LrrTLE:rOHX.--It is with much regret that we record the death of Dr. Thomas Herbert Litttejohn, Medical Officer of Health for Hampstead, at the early age of 38 )Years. Trained in public health work by his father, Sir Henry D. Littlejohn, whom he assisted for several years after he became qualified, he brought a considerable experience to the otfices of Medical Ot~cer of Health, first at Scarborough and afterwards at Hampstead, where he succeeded Dr. Edmund Gwynn. For some months his health had not been good, and unfortunately he had ~o resort to hypnotics to procm'e sleep, and after a dose of sulphonal taken on August 31st he never thoroughly recow~red consciousness, and died on Sept. 4th. We feel sure that the sincere sympathy of all our readers will be extended to a family whose members have been so closely and honourably associated with Pu~)lic Health, in their bereavement.
Notes on Meteorology
NOTES
31
ON METEOROLOGY.
Br W. H. SYMONS, M.D., D.P.H., Medical Officerof Health and City Meteorologistfor Ba~h. METEOROLOGYand meteorological instruments have always interested me ; and in the following notes I have endeavoured to bring together some points which I think may interest you. I shall assume that you are all observers, and acquainted with the forms of meteorological instruments and methods of using, as described in that excellen~ little book, Hints to Meteorological Observers, by W. Marriott, published by Edward Stanford for the Royal Meteorological Society, and, therefore, I may at once proceed with my remarks. Choice o/ a site ]or a Meteorological Station.--As a rule there is very little choice. The site has to be where continuity of observation is probable, and therefore usually in the ground of some public institution, except where the services of a paid observer are retained. Hence, it follows, many stations are badly placed. Many of the old records of rainfall are of little value, because the gauges were placed in most unsuitable positions. In giving evidence on behalf of the Bath Water Works, the late G. J. Symons stated that a correction of something 5ke 30 per cent would have to be made in forming any estimate from some of the records kept around Bath. Some of the earliest reliable readings, taken continuously for several years in this City, were the observations made by the first Medical Officer of Health, Dr. C. S. Barter, the rainfall from 1855 to 1868 being recorded in the first published annual report. His gauge was situated on the roof of his house in the Paragon. Fortunately, Dr. Barfer's records overlap those taken at the Royal Literary and Scientific Institution, and for two years did not differ materially. The latter station can hardly be considered ideal ; to keep the gauge away from children it was placed on the thermometer screen; the reservoir for rain water being in the screen, it is possible that the thermometric readings may be influenced by the temperature of the water contained in the reservoir. On the Continent it is customary to place the rain gauges five feet above ground; in England they should be one foot. Those placed five or ten feet above ground are said to collect about five per cent less rain than those placed on the ground, the wind carrying over the gauge. I have not found any regular difference between a gauge placed six feet and one placed one foot above ground. The Meteorological Society's Regulations require the rain gauge to be set in an open situatio~ away from trees, walls, and buildings, at
32
N o t e s on M e t e o r o l o g y
[P~biio IIealth
the very least as many feet away from their base as they are in height. My gauge at my old station was four times this distance from a wall, and yet I found that another gauge, placed twenty feet north of this, collected more rain when the rain was with u south wind. The sunshine recorder should be placed in such a position that the sun can shine upon the instrument the whole of the time it is above the horizon ; this is a condition very difficult to fulfil, as it must be also accessible for changing the curds. From north-east to northwest there must be no building or chimney more than 4° above the horizon, except due south, where u building 12° above the horizon will not obstruct. The recorder should be placed somewhere about the mean elevation of the district, the bright sunshine of which it is supposed to record. In Bath we suffer by having the recorder placed in the vu]ley, where the morning mists shut out some light. The four feet earth thermometer is another instrument not easy to place ; it ought to be where no shadow falls, and it must not be near any sewer. I had some difficulty in placing this instrument in the Institution gardens; the first spot I choose was a few feet south of the screen irt which the thermometers are kept, but I found it registered 9 ° above the temperature in my own garden : the waste water from the Hot Baths was carried off in a culvert a few feet away. Two other sites chosen were fomid to be influenced by sewers. It is also necessary to take into consideration the immediate subsoil, and to see that it is representative of the locality for which the return is made. But the earth thermometer need not be read precisely at 9 o'clock; an hour either side will make no perceptible difference; u record taken once a week is a useful record, when a daily visit to u suitable spot cannot be arranged for. The daily variation seldom exceeds half u degree, nor the weekly variation one and a half degrees Fahrenheit, ut four feet below the surface. Any thermometer which can be read to half u degree may be used us an earth thermometer, but I prefer to have them graduated like clinical thermometers to 0"2°; they can then be easily read to 0"1. They should have ]urge bulbs, and the bulb be embedded in some non-conducting material, such us paraffin. Messrs. Negretti und Zumbru make an earth thermometer which is very generally used. I t is completely encased in u glass tube protected b y rubber rings. The contaiuing iron tube, which is sunk in the ground, has to be wider than usual) but one seems to be able to take u good many liberties with the instrument used to measure temperatures at four feet below the surface. Using a one inch iron tube, I found that when the portion above the ground was heated to the temperature of boiling water for an hour or more, there was very little change of temperature at u depth of four feet---only a fraction of
October, 1905]
Notes on Meteorology
33
a degree--but at a depth of one foot below the sudace, changes in the temperature of the air distinctly agect the record. Therefore, I prefer to use a tube of non-conducting material, such as a glass tube. The tube should be closed at its lower end, and contain sufl3cient mercury to cover the bulb of the thermometer. A large glass tube is apt to be broken by expansion and contraction of the soil, and that portion above the surface must be protected by a metal tube. I have had one glass tube in use for several years, but it is only threefourths of an inch in diameter. The thermometer I use is an ordinary chemical thermometer graduated to one-fifth of a degree ; it is mounted in the case in which it was sold, the front part of the ease being cut away to expose the scale. No doubt a piece of bamboo cane would answer the same purpose as the case of the thermometer. Approximate records at one, two, and three feet may be obtained by suspending the four-feet thermometer in its own tube at these depths, allowing at least half-an hour for registering the temperature of each zone. For more correct readings the tube below the thermometer shoutd be plugged by a wooden plug, or, if for permanent records, by being filled wath earth or sand below the thermometer, to prevent currents of air influencing the temperature. For some months past I have taken daily readings of earth thermometers placed side by side: one a standard chemical therm.ometer, No. 12,209, in glass tube ; another hung in a thin copper tube, six inches proiecting above the surface; and another in a thick iron tube, twelve inches projecting above the surface ; a fourth similar to the standard, also mounted in a glass tube, but placed in a sandy soil, on the same plot of ground. The thermometers mounted in glass tubes showed that the temperature of the earth was failing at 1 p.m. ; the others would lead one to think it was rising ; the air temperature had risen 20 ° between 9 and 1 o'clock. Considerable alterations have been made at my own station, in that I have been able to secure a piece of land projecting 100 feet beyond the general line of gardens. The Stevenson's screen is freely exposed on the south and east, and 200 feet from any building in other directions. The subsN1 is blue gas rock about one foot below the surface of grass. At the Henrietta Park station we have one foot of soil upon sand and gravel, and the minimum on the grass is often considerably below that registered at Combe Park. I think this must be because there are no buildings within several hundred feet, and not because the soil is sandy. In m y own plot I have laid down a portion ten feet square with sand 18 inches deep directly on the rock, but with no soil or grass a b o v e ; t h e minimum thermometer, supported one inch above the surface of this sand, registers two or three degrees above the thermometer similarly exposed above grass; other thermometers 3
34
N o t e s on Meteorology
EXA~IPLE~ OF CLI~ATOLO(~ICAL STATIONS,
~r.bli. ~eslt~
Notes on Meteorology
October, 1~05]
35
upon asphalte and stone usually indicate intermediate temperatures, whale the thermometer placed on the screen and. one projecting from the screen, five feet six inches above the grass, show higher temperatures. The thermometer placed on the grass is very liable to be broken, and it would be an advantage if one could get the same information from a thermometer placed above the screen. The thermometer one foot below the surface in sand, registers three or four degrees below a similar thermometer in a loamy soil under grass in frosty weather. It is important to have 'one-foot earth thermolneters in glass and not in metal tubes, as otherwise the true temperature is not recorded. Fogs.--The density of fogs is n o t generally noted, and hence the records concerning fogs are almost meaningless. Nearly twenty years ago the !ate 5It. @. J. Symons wrote a strong plea for the establishment of fog gauges (Symons's Meteorological Magazine, xvii., 17), and suggested the erection of a slab painted alternately in white and black stripes~ the black stripes being ¼, ½, 1, 2, and 4 inches wide, separated by white stripes 6 inches wide; the black stripes to be numbered from one to five ; the amount of fog recorded to be that of the thinnest line which could be seen by an observer standing twenty feet in front of the scale. Such a meter may be suitable for the very opaque, small-grained London fog, the London particular as it is called, but for the coarse-grained fog one gets in the country, all the lines appear ahnost simultaneously as one approaches the scale, and I have not seen a fog in Bath when one could not see the whole of the scale at twenty feet, and, therefore, we may assmne we never get Fog 1 of G. J. Symons's scale. SCALE Outlines of objects visible at-- just
12 m i l e s 6
s
'.:
[
FOR
ESTIMATING
FOGS. Degree Visibility. of Fog.
0bj eets for Combe Park Station.
. . . .
V. 12 m . ""[
:::
"1 Combe Down, i~ath~i~pton D o w ,
12 f u r l o n g s ... ""! B e e c h e n Cliff, T w e r t o n R o u n d Hill ...IV- l ~ m . 6 ..... D e s t r u c t o r C h i m n e y , T w e r ~ o n C h i m n e y s I V. -~m . 3 ,: ...... i Locksbrook Chapel Steeple ...... V. ~ m . 1000 feet or 400 paces! A g a r d e n w a l l . . . . . . . . . . . . iV.400p. 500 , 200 , T r e e s b y brook . . . . . . . . . . . . V.200p. 250
,,
i00
,,
Garden
\vall
0
IV. 6 m . F. 1 ..IV. 3 ~. F. 2
. . . . . . . . . . . .
V.100p. F
F. F. F. F. F. F.
3 4 5 6 7 8
i understand the Meteorological Council have recently considered the establishment of a workable scale for estimating fog. I do not know what scale was suggested, but for some years I have used a scale based upon the limit of visibility ; a note being made of the distance
36
Notes on Meteorology
re~bl~ e ~ l t h
of various objects from the point of observation, the degree of fog being inversely as the distance. If I can see the outline of a hill six miles distant, but nothing beyond, I record F.1; if three mites distant F.2, etc. For dense fogs, some object belonging to the Meteorological Station may be used in determining the limit of visibility; the character of the back-ground will influence the result ; a light-coloured object, such as the Stevemson's screen, disappears from view before a dark object, such as the cups of Robinson's anemometer, or the stand of black bulb thermometer. The densest fog in Bath last year was on November 15th, at 9 a.m. I could see the screen at 50 feet but not at 52 feet; the cups of a low-level anemometer were visible at 70 feet. The ¼ inch line on Mr. G. J. Symons's scale could be seen at 50 feet, the 4-inch line at 80 feet. This fog was registered as F.10. Visibility 50 paces = F.9 ; visibility 25 paces = F.10 ; visibility 12 paces - F.20 ; visibility 6 paces F.30 ; visibility 3 paces :: FA0. At night, street lamps are convenient units of measurement, if their distance is known in paces. Visibility in a dense fog is easily determined to a pace, but fogs are usually patchy, and dense fogs vary from minute to minute, and also in different directions. I record the greatest density; it may be fairly clear in the north towards Lansdown, while on the south over the valley we may have F.6. Sometimes, however, it is foggy at high levels and quite clear at low levels ; generally we get more fog in the suburbs of Bath than we do in the city. I should regard a fog in which I could not see a man at 50 paces, in the day time, as an extremely dense fog for Bath. There was only one such fog during the past year, but in a dense London fog we may be tmabte to see a mart at 5 paces; one of the advantages of living in London is said to be you can see what you breathe° During 1904 1 registered fog on 61 days at Combe Park, namely: 5 times F.1, 15 1~.2, 20 F.3, 10 F.4, 2 F.5, 3 F.6, 2 F.7, 3 F.8, and 1 F.10. Only on six days was it so foggy at 9 a.m. that I could not see the outline of trees or houses 1,000 feet away in the valley of the Bath Avon. Captain Carpenter, in his report to the Meteorological Council, says: " T h e r e is no evidence of any special connection between the frequency or intensity of fogs and geological conditions, nor does the locality of the commencement of fog depend upon geological formation." " No severe fog occurred with an air temperature above 40° F." My limited observations lead me to think geological and physiographical conditions have much to do with the formation of fog, but the fog may be fairly evenly distributed after formation. Broadly speaking, an air temperature below 40 ° , an earth or river temperature
October, 19o5]
Notes
on Meteorology
37
above 40°, a more or less stagnant atmosphere, and the presence of dust particles in the air, are the four principal conditions tending to produce fog. Dust.--The estimation and examination of dust is rather outside the rotltine work of meteorology, but is of much importance and interest, and regular observations of the amount of coarse dust which falls in our streets would be interesting; but possibly our rainfall records answer nearly as well. Hesse's tubes and Petrie's dishes are commonly used for collecting dust in rooms, but these appliances are not suitable for estimating dust coming from a destructor or from building operations. In investigating a nuisance of this kind, one Medical Officer of Health used wooden frames, one yard square and six inches deep, placed on American cloth; the amount of dust collected daily or weekly being noted, and its quality determined microscopically. I have tried this method for comparing the amount of dust which falls in the centre of the City, and in m y front and back gardens at Combe Park, but a shower of rain upsets the record. I have also a zinc tray, one yard square and two inches deep, which i have used for tNs purpose; this is also useful for collecting dew. A more accurate plan for dust is to draw a known quantity of air through a suitable filter. I have used the paper candles sold for Soxhlet's Fat Extractors, and also a Pasteur's porcelain filter for this purpose, but a glass tube plugged with sulphate of potassium crystals and powder is perhaps the best filter.* The air is drawn through the filter by means of a water pump, the volume being measured by a small gas meter; the pump and meter may be in the house, and the filter a hundred feet or more away, the air being drawn through a ¼ inch compo pipe laid under ground. Mter filtration the air may be examined for amount of CO~, etc. Such observations are made regularly in Paris, but, as far as I know, not in England. Some years ago I had three such stations working at various levels around Bath, but want of time and assistance made me drop the work. Local currents coming from chimneys upset my estimation of CO.2. Evaporation.--The official evaporation tank is six feet square and two feet deep. This should be sunk in the ground, with the top level with the blades of grass, and should be kept filled with water to within about three inches of the rim. I t is not an easy matter to measure accurately the level of the water, on account of the movement caused by wind. I prefer to take the reading from a graduated gauge tube, which is in communication with the tank ; it is quite easy to read the * Sulphate of potassium being a soluble sMt does no~ interfere with the subsequent microseopieM examination of the dust nor with the estimation of organic matter.
33
Notes on Meteorology
~p~bn~ ~ t ~
level in the tank to one-twentieth of an inch. The tube must be capable of being closed by a tap. The gauge tube may be several feet away from the tank, where the ground is low enough to allow the observer to stoop easily to bring his eye on a level with the graduation of the tube. It is convenient to have a pit six feet away from the tank. After observing the level the water in the tube may be blown back into the tank and the tap closed, to prevent fracture of the glass by frost. The loss by evaporation for 1903 was t8 inches. Ozone.--The determination of ozone is not now included by the Royal Meteorological Society in its scheme of ordinary observagons, because the test papers employed are frequently unreliable. Mr. G. J. Symons thought it was a pity these observations were given up. He had papers placed in various parts of London, and had them returned to him for examination once a month. He found that winds from the country coloured the paper ; the winds which had passed over the metropolis never did. It does not need a large town to deprive the air of this property. When the wind is westerly the paper at our eastern station is not coloured, and when the wind is easterly the paper at the east station is coloured much more than that at the west station, although the west station is 100 feet above the east station, i[ find that paper exposed on the dome of the Guildhall is less coloured than the low level paper. Papers should be wetted, and the colour estimated as soon after removing from the screen as possible; but papers from various stations should be compared simultaneously. In preparing ozone papers I use white blotting paper. The sheets are cut into quarter demy, washed with a 5 per cent solution of P.B. hydrochloric acid, and then rinsed with water until quite free from acid, then dried. The starch compound is prepared by heating 5 grams of arrowroot with 200 co. of water, and adding 1 grant of potassium iodide. Twenty co. of this mixture is spread on each quarter sheet of paper, on a glass plate, and the paper thrown on to a wire to dry; then cut into slips, made up in books, and wrapped in tinfoil. Such paper may be kept for many years. Wind Direction.--It may seem a very easy matter to determine the direction of the wind, but practically this is by no means easy as regards light winds. Eddies caused by buildings are very troublesome ; smoke from a tall chimney is perhaps the best guide ; smoke from the ordinary house chimney is a very poor guide; if we observe three or four chimneys close together, the smoke may have a different direction from each one. In order to get the true direction the chimney top or vane must be forty feet above the buildings. The Pressure Tube Anemometer shows how the force of the wind
0~tob~, ~90,5?
Notes
on Meteorology
39
varies from second to second. When travelling more than ten miles an hour, it appears to be thrown wavelike against obstacles; the pressure is not continuous. Change in the direction of ~he wind is proverbially common, and 9 a.m. records are of little value ; probably more information can be gained by studying barometric gradients; the true direction o~ the wind is shown in the daily weather charts in this way, and also its force. It is quite easy to make seif-reeording anemoscopes, but, as before stated, difficult to fix them in suitable places. Messrs. Lander and Smith, of Canterbury, are now introducing a sebes of cheap recording meteorological instruments, which should prove very usdul to Medical 0t~cers of Health in checking the returns which they receive from various sources. It is surprising how few persons can take twenty consecutive daily readings of any inst,'ument without maNng a mistake; usuMly with thermometric readi *,he mistake is one of 5 ° or 10°, and with the barometric readings h. inch; such errors are easily corrected by se!f-reeording instrmnents, which are perhaps not su~ciently sensitive to entirely replace the non-recording instruments. Sun Spots.--The terrific storms which go on in the photosphere do not appear to imquence terrestrial atmospheric conditions, except as regards magnetic storms. But magnetic storms may have some influence on living organisms. I have endeavoured to keep a record d large sun spots duiing the past year, but fortunately it is easy to obtain early in March an accurate record of the position and magnitude of each group of sun spots for each day of the preceding year in the Greenwich Photo-Hdiog~aphic Results. Dm C. H. CAYLEY, one of the Divisional Health Officers of Bombay, some little time ago hurt one of his fingers, tetanus developed, and he died after a few days' illness. Dr. Cayley went out several years ago for plague work, but was subsequently elected by the Bombay Municipality as one of its Health Officers. DEATh OF DR. T. It. LrrTLE:rOHX.--It is with much regret that we record the death of Dr. Thomas Herbert Litttejohn, Medical Officer of Health for Hampstead, at the early age of 38 )Years. Trained in public health work by his father, Sir Henry D. Littlejohn, whom he assisted for several years after he became qualified, he brought a considerable experience to the otfices of Medical Ot~cer of Health, first at Scarborough and afterwards at Hampstead, where he succeeded Dr. Edmund Gwynn. For some months his health had not been good, and unfortunately he had ~o resort to hypnotics to procm'e sleep, and after a dose of sulphonal taken on August 31st he never thoroughly recow~red consciousness, and died on Sept. 4th. We feel sure that the sincere sympathy of all our readers will be extended to a family whose members have been so closely and honourably associated with Pu~)lic Health, in their bereavement.