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On the effect of the pressure of the atmosphere on the mean level of the ocean
394
2deehanics, Physics~ and Chemistry.
This clearance at each end of the ~iston amounts to 0"23 feet, by the area of the piston. Hence we h a v e ~ With the fan3766X(2"57-}-'23).= 1255. 840 Without the fan 3575 × (1"86@'23) 870. 853 The 'numbers 840 and 853 being the respective volumes of steam at 16"83 and 16.31 lbs. per square inch. Then 870 : 1255 : : 100 : 1'44, (rr, gain for whole period, 44 per ct. To show the comparison at the time of' the last observati6n in each watch, which would be more nearly a criterion than the mean performance, we have, (taking the average revolutions per minute, instead of the total number,) With the fan 16"10X(2.80-~.23)= 0"5880. 829 Without the fan --14× (1-60-~'23) ~ 0"3046. 841 Then, 0"3046 : 0'5880 : : 1"000 : 1"927 ; or, the evaporative effect was nearly doubled, and the speed of the ship (engine) increased as 14 : 16"10, or about two statute miles per hour. In the above ealculalions, no account is taken of the steam used by the engine driving the fan, which may be estimated as equal to about one-fourth the main cylinder full of steam per minute, and would amount to about ~ per cent. in the first, and 2 per cent. in the second case. It is not claimed that these results would be at all extraordinary if produced by blowers in the usual manner; but when it is considered that they are produced with a ve~T trifling expenditure of power, without waste of tirol, without any destructive" influence on the furnaces, that both the fires and the blowing machinery are perfectly accessible for cleaning at all times, and, in short, that all the well known advantages of natural draft are combined with the power of nearly doubling the evaporation in calm weather, I think the results show an improvement sufficiently marked to be worthy a place in this Journal.
On the Ebrect of the Pressure of the dtmo~phere on the ~lean Level of the Ocean. By CAPTAIN Silt ~hIvIES CLARK Ross, R.N., F.R.S. The author states that, in September 1848, Her Majesty's ships Enter. pr~se aoad Investigator having anchored in the harbor of Port Leopold, in tat. 74 N. and long. 91 ° W., a heavy pack of ice was driven down upon and completely closed the harbour's mouth, thus effectually preventing their egress, and compelling them there to pass the winter of 1848-49. It was during that period that the series of observations here presented to the Royal Society was obtained ; and, as the observations were made under peculiarly favorable circumstances, t~,e author considFrom the Lond., Edin. and Dub. Philos. Mag, Oct. 1854.
Pressure of the Atmosphere on the ,Mean Level of lhe Ocean.
395
ors they wilt throw some light on the movements of the tides~ and on some of the causes of their apparent irregularities. Soon after the harbor had been completely frozen over, a very heavy pressure from"the main pack forced the newly-formed sheet of ice, which covered the bay, far up towards its head, carrying the ships with" it into such shallow water that at tow spring-tides their keels sometimes rested on the ground. Under these circumstances the movements of the tides became to the author an object of great anxiety, and consequently of carefill observation, in order to ascertain the amount of irregularities to which they were liable in that particular locality. The first few days' observations evidenced much larger differences in the elevation or depression of successive high or low-waters than could be accounted for by any of the generally received causes of disturbance ; and lhe author was at once led to connect them with changes of the pressure of the atmosphere, from perceiving that on the days of great atmospheric pressm'e high-water was not so high as it ought to have been, and tow-water was lower than its proper height ; and that the reverse took place on the days of smaller pressure. As it was found that the usual method of determining the mean level of the sea, by taking the mean of successive high and low-waters, was inadequate to the detection of small quantities arising fi'om a change in the pressure, a system of observation was adopted different from that heretofore practised, in order to determine th'e mean level of' the sea on each day. In the first instance, simultaneous observations of the height of the tide and of the mercury in the barometer were made every.quarter of an hour throughout the twenty-four h6urs. From these it was found that the mean level of the sea for each day could be determined with great aceuraey~ and that the ~'ariation in the daily mean level and in the mean pressure of the atmosphere followed each other in a remarkable manner, so that a rise in the former corresponded to a diminution in the latter. Subsequently, however, hourly observations were adopted. The peculiar advantages of the position of the ships at Port LeoDold for makingtidal observations are stated to have eons{sted in : ~ i. the ~,reat width of the entrance of the harbor admitting the free ingress and egress of the water, combined with the large field of ice which covered the whole of the bay~ eompletely subduing every undulation of the water. 2. The steady movement of the immense platform of ice, rising and •falling with such singular regularity and precision as to admit the reading offthe marks of the tide-pole with the greatest exactness~ even to tt~ tenth of an inch. 3. The shallowness of the water and the evenness and solidity of the clay bottom admitting the fixture of the tide-pole ~,'ith immoveabte firmness. 4. The whole surface of the sea in the neighborhood being, for the greater part of the time, covered by a sheet of ice, preventing those irre.gularities which occur in other localities from the violence of the wind raising or depressing the sea in as many different degrees as it varied in strength or duration.
2dechanicsi P]~ysics, and Chemistry. For fixing the tide-pole for the "Enterprise~" a hole 2 feet square was
396
cut through the icy platform, and a strong pole, nearly 40 feet long, Was passed through it and dri~.'en firmly down several feet into the clay, be. ing fixed by heavy iron weights, ~ hich also rested.on the clay and pre. vented any movement of the po~e. "It was placed in.about21 feet depth of water at the time of mean level of the sea. Another such tide-pole tvas, in a like manner, fixed through a hole in the ice close to the "In. vestizator," for the sake of reference and comparison. Hourly observations of the height of the tide and of the barometer were commenced on the 1st of November, and were continued by the officers of each ship throughout the whole of the nine following months to the end of July. After forty-seven days of observation, an interruption in one of the series occurred in consequence of the tide-pole of the "Ente~TTise,, having been drawn up by the ice, to the under part of which• it had become f?ozen. The amount of displacement of the pole was easily determined by a comparison with that of the "Investigator," but several days elapsed before it could be satisfactorily fixed at the same point in which it had been originally. The observations of these forty-seven days are those which are given in the paper, and their discussion is the immediate object of the communication. It is stated that subsequent observalions seem to show that, from the time of the interruption to the middle of July, there was a progressive elevation of the mean level of the sea, which, although of small amount~ was sufficiently evident from month to month to render the subdivision of the series desirable, in order that the individual observations of each separate division shouhl be strictly comparable. The height of the sea and the corresponding height of the mercury in the barometer, at every hour in each day, f?om the 1st November to the 18th December, 1848, are given in tables. In these arithmetic mean of the hourly heights of the sea fbv each day is taken as the mean level of the sea for that day, and the mean of the hourly heights of the barometer is taken as the corresponding height of the barometer. These mean levels and corresponding mean barometric heights are given in another twocolumn table, arranged in the order of the days of' observation ; and in a third table these are arranged in the order of the heights of the barometer with the corresponding mean levels, without regard to the dates of observation, for the purpose of showing the dependence which the latter have on the former. On these tables the author makes the following remarks. The fortyseven days of hourly, observations give for the mean height of the barometer 29"874 inches, and of the mark of mean level of~he sea 21 feet 0"21 in. The mean of three days ~ 30 227 greatest pressure w~s: 5 ' ~and of corresponding level ~0 feet 8'4 inch. TheleastmeanpressureOf threewasdays: I 29'559~ and of corresponding level 21 feet 5.4 inch. Diff. -t-0"668
Diff. ~ 9 ' 0
Thus a difference of pressure equal to 0-668 inch produced a difference of 9 inches in the mean level of the sea. As the ratio of 9 to .668 is
Phonic Signals in .heavigation.
397
13"467 to 1, the author considers that the effect of the pressure of the atmosphere on the level of the sea is 13,467 times as great as the effect it produces on the mercury in the barometer, or very nearly in the inverse ratio of the specific gravities of sea-water and mercury. He however states, that this remarkable coincidence must be considered in a great measure accidental, for if a greater number of days' observation be taken in order to deduce the mean greatest and mean least pressure, and the corresponding mean levels, a different result will be obtained. From these observations, however, he considers that he has been enabled to deduce results which plainly point to the law which governs the effect of the pressure of the atmosphere on the mean level of the sea, and may be encouraged to pursue the investigation through a more extended series of observations, in order to arrive at the most accurate conclusion that the observed facts may justify. In conclusion, a formula is given for determining the correct height of the tide, or of the mean level of the sea : ~ Let L denote the correct height of the tide, or of the m e a n level of the sea; B the m e a n pressure of the atmosphere ; ~ t~e observed height of the tide, or of the m e a n level of the sea; the corresponding height of the barometer ; I) the ratio of the specific gravity of mercury to that of sea-water : then L=~nL.(fl--B) D.
Examples are given of the application of this formula. F o r the J ournal of the Franklin Institute.
Rernarks upon the Use of Phonic Signals in .Navigation. By Prof. JoH~ C. CR~sso~, C. E. Among the numerous suggestions, elicited by the melancholy loss of the steamer .~rctic, for the prevention of such disastrous collisions, there is none that appears so easily attainable as the use of the steam whistle, or, more correctly, steam trumpet. The proper mode of using this instrument being, therefore, a matter of some importance, a few remarks, based upon experimental knowledge, may be a not inappropriate contribution to the pages of the Journal. It is well known that the blast of a large steam trumpet is disti,nctly audible at the distance of five miles, and instances are known of its being heard at more than:twice that distance in cloudy weather. It has been found, also, that this peculiarly abrupt smmd is well adapted for the formation of distinct echoes, and at sea its echo from a bluff coast or a ship is very remarkable, so as to be quite startling when heard for the first time in darkness or fog. The writer took part in some trials ot it on the Bay of Fun@, which proved that this echo would give notice of approach to a rocky headland, distant several miles, and of a small schooner more than a mile off. May not these qualities of the steam trumpet be so applied as to make it not only give a warning signal to others outside the ship, but also to return the warning to the ship giving it ? If s% how is it best to be accomplished ? go~, X X V I I I , - - : r m ~ D SzaiEs.--No. 6 , ~ D ~ Z E . ~ R , IS54.
34
2deehanics, Physics~ and Chemistry.
This clearance at each end of the ~iston amounts to 0"23 feet, by the area of the piston. Hence we h a v e ~ With the fan3766X(2"57-}-'23).= 1255. 840 Without the fan 3575 × (1"86@'23) 870. 853 The 'numbers 840 and 853 being the respective volumes of steam at 16"83 and 16.31 lbs. per square inch. Then 870 : 1255 : : 100 : 1'44, (rr, gain for whole period, 44 per ct. To show the comparison at the time of' the last observati6n in each watch, which would be more nearly a criterion than the mean performance, we have, (taking the average revolutions per minute, instead of the total number,) With the fan 16"10X(2.80-~.23)= 0"5880. 829 Without the fan --14× (1-60-~'23) ~ 0"3046. 841 Then, 0"3046 : 0'5880 : : 1"000 : 1"927 ; or, the evaporative effect was nearly doubled, and the speed of the ship (engine) increased as 14 : 16"10, or about two statute miles per hour. In the above ealculalions, no account is taken of the steam used by the engine driving the fan, which may be estimated as equal to about one-fourth the main cylinder full of steam per minute, and would amount to about ~ per cent. in the first, and 2 per cent. in the second case. It is not claimed that these results would be at all extraordinary if produced by blowers in the usual manner; but when it is considered that they are produced with a ve~T trifling expenditure of power, without waste of tirol, without any destructive" influence on the furnaces, that both the fires and the blowing machinery are perfectly accessible for cleaning at all times, and, in short, that all the well known advantages of natural draft are combined with the power of nearly doubling the evaporation in calm weather, I think the results show an improvement sufficiently marked to be worthy a place in this Journal.
On the Ebrect of the Pressure of the dtmo~phere on the ~lean Level of the Ocean. By CAPTAIN Silt ~hIvIES CLARK Ross, R.N., F.R.S. The author states that, in September 1848, Her Majesty's ships Enter. pr~se aoad Investigator having anchored in the harbor of Port Leopold, in tat. 74 N. and long. 91 ° W., a heavy pack of ice was driven down upon and completely closed the harbour's mouth, thus effectually preventing their egress, and compelling them there to pass the winter of 1848-49. It was during that period that the series of observations here presented to the Royal Society was obtained ; and, as the observations were made under peculiarly favorable circumstances, t~,e author considFrom the Lond., Edin. and Dub. Philos. Mag, Oct. 1854.
Pressure of the Atmosphere on the ,Mean Level of lhe Ocean.
395
ors they wilt throw some light on the movements of the tides~ and on some of the causes of their apparent irregularities. Soon after the harbor had been completely frozen over, a very heavy pressure from"the main pack forced the newly-formed sheet of ice, which covered the bay, far up towards its head, carrying the ships with" it into such shallow water that at tow spring-tides their keels sometimes rested on the ground. Under these circumstances the movements of the tides became to the author an object of great anxiety, and consequently of carefill observation, in order to ascertain the amount of irregularities to which they were liable in that particular locality. The first few days' observations evidenced much larger differences in the elevation or depression of successive high or low-waters than could be accounted for by any of the generally received causes of disturbance ; and lhe author was at once led to connect them with changes of the pressure of the atmosphere, from perceiving that on the days of great atmospheric pressm'e high-water was not so high as it ought to have been, and tow-water was lower than its proper height ; and that the reverse took place on the days of smaller pressure. As it was found that the usual method of determining the mean level of the sea, by taking the mean of successive high and low-waters, was inadequate to the detection of small quantities arising fi'om a change in the pressure, a system of observation was adopted different from that heretofore practised, in order to determine th'e mean level of' the sea on each day. In the first instance, simultaneous observations of the height of the tide and of the mercury in the barometer were made every.quarter of an hour throughout the twenty-four h6urs. From these it was found that the mean level of the sea for each day could be determined with great aceuraey~ and that the ~'ariation in the daily mean level and in the mean pressure of the atmosphere followed each other in a remarkable manner, so that a rise in the former corresponded to a diminution in the latter. Subsequently, however, hourly observations were adopted. The peculiar advantages of the position of the ships at Port LeoDold for makingtidal observations are stated to have eons{sted in : ~ i. the ~,reat width of the entrance of the harbor admitting the free ingress and egress of the water, combined with the large field of ice which covered the whole of the bay~ eompletely subduing every undulation of the water. 2. The steady movement of the immense platform of ice, rising and •falling with such singular regularity and precision as to admit the reading offthe marks of the tide-pole with the greatest exactness~ even to tt~ tenth of an inch. 3. The shallowness of the water and the evenness and solidity of the clay bottom admitting the fixture of the tide-pole ~,'ith immoveabte firmness. 4. The whole surface of the sea in the neighborhood being, for the greater part of the time, covered by a sheet of ice, preventing those irre.gularities which occur in other localities from the violence of the wind raising or depressing the sea in as many different degrees as it varied in strength or duration.
2dechanicsi P]~ysics, and Chemistry. For fixing the tide-pole for the "Enterprise~" a hole 2 feet square was
396
cut through the icy platform, and a strong pole, nearly 40 feet long, Was passed through it and dri~.'en firmly down several feet into the clay, be. ing fixed by heavy iron weights, ~ hich also rested.on the clay and pre. vented any movement of the po~e. "It was placed in.about21 feet depth of water at the time of mean level of the sea. Another such tide-pole tvas, in a like manner, fixed through a hole in the ice close to the "In. vestizator," for the sake of reference and comparison. Hourly observations of the height of the tide and of the barometer were commenced on the 1st of November, and were continued by the officers of each ship throughout the whole of the nine following months to the end of July. After forty-seven days of observation, an interruption in one of the series occurred in consequence of the tide-pole of the "Ente~TTise,, having been drawn up by the ice, to the under part of which• it had become f?ozen. The amount of displacement of the pole was easily determined by a comparison with that of the "Investigator," but several days elapsed before it could be satisfactorily fixed at the same point in which it had been originally. The observations of these forty-seven days are those which are given in the paper, and their discussion is the immediate object of the communication. It is stated that subsequent observalions seem to show that, from the time of the interruption to the middle of July, there was a progressive elevation of the mean level of the sea, which, although of small amount~ was sufficiently evident from month to month to render the subdivision of the series desirable, in order that the individual observations of each separate division shouhl be strictly comparable. The height of the sea and the corresponding height of the mercury in the barometer, at every hour in each day, f?om the 1st November to the 18th December, 1848, are given in tables. In these arithmetic mean of the hourly heights of the sea fbv each day is taken as the mean level of the sea for that day, and the mean of the hourly heights of the barometer is taken as the corresponding height of the barometer. These mean levels and corresponding mean barometric heights are given in another twocolumn table, arranged in the order of the days of' observation ; and in a third table these are arranged in the order of the heights of the barometer with the corresponding mean levels, without regard to the dates of observation, for the purpose of showing the dependence which the latter have on the former. On these tables the author makes the following remarks. The fortyseven days of hourly, observations give for the mean height of the barometer 29"874 inches, and of the mark of mean level of~he sea 21 feet 0"21 in. The mean of three days ~ 30 227 greatest pressure w~s: 5 ' ~and of corresponding level ~0 feet 8'4 inch. TheleastmeanpressureOf threewasdays: I 29'559~ and of corresponding level 21 feet 5.4 inch. Diff. -t-0"668
Diff. ~ 9 ' 0
Thus a difference of pressure equal to 0-668 inch produced a difference of 9 inches in the mean level of the sea. As the ratio of 9 to .668 is
Phonic Signals in .heavigation.
397
13"467 to 1, the author considers that the effect of the pressure of the atmosphere on the level of the sea is 13,467 times as great as the effect it produces on the mercury in the barometer, or very nearly in the inverse ratio of the specific gravities of sea-water and mercury. He however states, that this remarkable coincidence must be considered in a great measure accidental, for if a greater number of days' observation be taken in order to deduce the mean greatest and mean least pressure, and the corresponding mean levels, a different result will be obtained. From these observations, however, he considers that he has been enabled to deduce results which plainly point to the law which governs the effect of the pressure of the atmosphere on the mean level of the sea, and may be encouraged to pursue the investigation through a more extended series of observations, in order to arrive at the most accurate conclusion that the observed facts may justify. In conclusion, a formula is given for determining the correct height of the tide, or of the mean level of the sea : ~ Let L denote the correct height of the tide, or of the m e a n level of the sea; B the m e a n pressure of the atmosphere ; ~ t~e observed height of the tide, or of the m e a n level of the sea; the corresponding height of the barometer ; I) the ratio of the specific gravity of mercury to that of sea-water : then L=~nL.(fl--B) D.
Examples are given of the application of this formula. F o r the J ournal of the Franklin Institute.
Rernarks upon the Use of Phonic Signals in .Navigation. By Prof. JoH~ C. CR~sso~, C. E. Among the numerous suggestions, elicited by the melancholy loss of the steamer .~rctic, for the prevention of such disastrous collisions, there is none that appears so easily attainable as the use of the steam whistle, or, more correctly, steam trumpet. The proper mode of using this instrument being, therefore, a matter of some importance, a few remarks, based upon experimental knowledge, may be a not inappropriate contribution to the pages of the Journal. It is well known that the blast of a large steam trumpet is disti,nctly audible at the distance of five miles, and instances are known of its being heard at more than:twice that distance in cloudy weather. It has been found, also, that this peculiarly abrupt smmd is well adapted for the formation of distinct echoes, and at sea its echo from a bluff coast or a ship is very remarkable, so as to be quite startling when heard for the first time in darkness or fog. The writer took part in some trials ot it on the Bay of Fun@, which proved that this echo would give notice of approach to a rocky headland, distant several miles, and of a small schooner more than a mile off. May not these qualities of the steam trumpet be so applied as to make it not only give a warning signal to others outside the ship, but also to return the warning to the ship giving it ? If s% how is it best to be accomplished ? go~, X X V I I I , - - : r m ~ D SzaiEs.--No. 6 , ~ D ~ Z E . ~ R , IS54.
34