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Manganese as a plant food
CURRENT
712
TOPICS.
[J. F. I.
The Survey of the Stars. J. H. JEAKS. (ijratrhre, March 12. 1927.)-When the Gold Medal of the Royal Astronomical Society was awarded to Prof. Frank Schlesinger for his accomplishments in stellar parallax and astronomical photography, it was fitting that a historical survey should be given of the field that the American The first part of the astronomer has made so peculiarly his own. Then, tribute having been renaddress is of rare literary charm. dered to Urania, the development of the idea of parallax is considered. Ptolemy founded his belief that the earth was the centre about which the celestial spheres turned upon the absence of that parallactic motion which should have manifested itself, if the earth moved. Hooke, Roemer and Bradley all tried in vain to discover displacement of the stars due to the motion of our planet. Suddenly in 1838 the existence of parallax was definitely established and not by a single astronomer but by three working independently, Bessel, Struve and Henderson. These found different parallaxes for 61 Cygni, a Lyra and a Centauri. Thus these three stars were proved to be at different distances from the earth. Progress in the measurement of additional parallaxes was, however, slow, so slow indeed that in 1g01 Simon Newcomb’s list of stars with known parallaxes contained only 72, of which 15 were doubtful. Two years after this Schlesinger commenced his publication of parallaxes determined by photographic methods. Seven observatories coijperated in the work with the result that his 1924 “ General Catalogue of Parallaxes ” lists 1870 stars, Here it is rare that the probable error of a parallax exceeds I/IOO of a second, “ the angle subtended by a pin-head at a distance of twenty miles,” whereas the average error in Newcomb’s time was 1/20 second. Let a series of spheres be described about the sun as a centre with radii equal to I, 2, 3, 4, 5, etc., parsecs, the parsec being the distance at which a star has a parallax of one second, viz., 19,1oo,ooo,ooo,ooo miles. No star has been found as near to the sun as I parsec. Three lie within a radius of 2 parsecs, six within 3 and eighteen within 4 parsecs. If stars are scattered uniformly through space there should be 280 within IO parsecs of the earth, on the supposition that all have been found that exist within a radius of 4 parsecs of the sun, but of these 280 Schlesinger’s catalog contains only 86. Likewise within a radius of IOO parsecs 281,250 stars should be situated. “ At the present rate of progress the determination of their parallaxes would occupy astronomLf; fsully 1000 years to come.” . .L. Manganese
as a Plant Food.- OSWALLI SCHREINEK and PAUL a+zd Eng. Chenz., 1927, 19, 40~404) find that a sulphate) must be present in the manganese salt (e.g., manganous soil in order to produce normal growth of tomato plants and a crop of their fruit. J. S. H. R. DAWSON (Ind.
712
TOPICS.
[J. F. I.
The Survey of the Stars. J. H. JEAKS. (ijratrhre, March 12. 1927.)-When the Gold Medal of the Royal Astronomical Society was awarded to Prof. Frank Schlesinger for his accomplishments in stellar parallax and astronomical photography, it was fitting that a historical survey should be given of the field that the American The first part of the astronomer has made so peculiarly his own. Then, tribute having been renaddress is of rare literary charm. dered to Urania, the development of the idea of parallax is considered. Ptolemy founded his belief that the earth was the centre about which the celestial spheres turned upon the absence of that parallactic motion which should have manifested itself, if the earth moved. Hooke, Roemer and Bradley all tried in vain to discover displacement of the stars due to the motion of our planet. Suddenly in 1838 the existence of parallax was definitely established and not by a single astronomer but by three working independently, Bessel, Struve and Henderson. These found different parallaxes for 61 Cygni, a Lyra and a Centauri. Thus these three stars were proved to be at different distances from the earth. Progress in the measurement of additional parallaxes was, however, slow, so slow indeed that in 1g01 Simon Newcomb’s list of stars with known parallaxes contained only 72, of which 15 were doubtful. Two years after this Schlesinger commenced his publication of parallaxes determined by photographic methods. Seven observatories coijperated in the work with the result that his 1924 “ General Catalogue of Parallaxes ” lists 1870 stars, Here it is rare that the probable error of a parallax exceeds I/IOO of a second, “ the angle subtended by a pin-head at a distance of twenty miles,” whereas the average error in Newcomb’s time was 1/20 second. Let a series of spheres be described about the sun as a centre with radii equal to I, 2, 3, 4, 5, etc., parsecs, the parsec being the distance at which a star has a parallax of one second, viz., 19,1oo,ooo,ooo,ooo miles. No star has been found as near to the sun as I parsec. Three lie within a radius of 2 parsecs, six within 3 and eighteen within 4 parsecs. If stars are scattered uniformly through space there should be 280 within IO parsecs of the earth, on the supposition that all have been found that exist within a radius of 4 parsecs of the sun, but of these 280 Schlesinger’s catalog contains only 86. Likewise within a radius of IOO parsecs 281,250 stars should be situated. “ At the present rate of progress the determination of their parallaxes would occupy astronomLf; fsully 1000 years to come.” . .L. Manganese
as a Plant Food.- OSWALLI SCHREINEK and PAUL a+zd Eng. Chenz., 1927, 19, 40~404) find that a sulphate) must be present in the manganese salt (e.g., manganous soil in order to produce normal growth of tomato plants and a crop of their fruit. J. S. H. R. DAWSON (Ind.