ASTRONOMICAL PROGRESS AND PHENOMENA. 



35 



V. Riley, of "Washington, on the hop aphis, 

 the Phorodon humuli, and one by Prof. Charles 

 A. Young, of Princeton, on the work done by 

 his party in observing the eclipse of the sun at 

 a station in Russia. Sir William Thompson 

 read a paper on the Vortex Theory of the 

 Luminiferous Ether. This showed mathemati- 

 cally that a perfect fluid completely enwrapped 

 in minute vortices would do everything that 

 the luminiferous ether was called on to do. 

 The paper had its origin in the theory proposed 

 by Prof. Fitzgerald, of Dublin. It is regarded 

 as one of the events of the meeting, and as 

 marking the nearest approach yet made to the 

 mathematical conception of the ether. 



Several committee reports were read on solar 

 radiation, magnetic observations, electrolysis, 

 and other subjects. 



Various public lectures were given. Prof. 

 H. B. Dixon spoke on "The Rate of Explo- 

 sions " ; Prof. George Forbes gave a working- 

 men's lecture on " Electricity " ; Sir Francis 

 de Winton spoke on u Exploration in Central 

 Africa." 



In connection with Section H, an anthropo- 

 metric laboratory has been established. Many 

 of the members of the Association were here 

 weighed, measured, and subjected to various 

 tests to obtain data as to the statistics of the 

 cultivated class to compare with those gathered 

 from all classes, by Mr. Francis Galtoii, of 

 South Kensington. 



Grants. The total grants for researches made 

 by the Association amounted to 2,025, ranging 

 from 5 to 200 each, and divided among all 

 the branches. 



ASTRONOMICAL PROGRESS AND PHENOMENA. 

 During 1887 the usual steady advance was 

 made in all departments of astronomy, but at- 

 tention was specially concentrated upon celes- 

 tial photography and the total solar eclipse of 

 August 19. Among the notable events of the 

 year was the twelfth meeting of the Inter- 

 national Astronomische Gesellschaft, which 

 was held at Kiel, from August 29 to August 31, 

 under the presidency of Dr. Auwers. 



Instruments and Methods. In volume xvii of 

 the "Annals" of the Harvard College Observa- 

 tory, S. C. Chandler has published a descrip- 

 tion and theory of his " almucantar," and a 

 reduction and discussion of a long series of ob- 

 servations made with it in 1884-'85. The in- 

 strument, which belongs to the equal-altitude 

 class, consists of a telescope mounted upon a 

 base floating in mercury, and the observations 

 are made by noting the times when stars cross 

 the horizontal circle defined by the wire sys- 

 tem of the telescope. In the hands of the 

 inventor this instrument has given most ex- 

 cellent results ; but experience alone can decide 

 whether it will prove superior to the ordinary 

 zenith telescope in the hands of other persons. 

 Be that as it may, equal-altitude instruments 

 enjoy such a remarkable immunity from sys- 

 tematic errors, that astronomers must ulti- 

 mately have recourse to them in order to elim- 



inate the small systematic errors inseparable 

 from meridian work. 



M. Loewy, of the Paris Observatory, has pro- 

 posed a method of determining the constant of 

 aberration from differential measurements of 

 the changes in the distances of suitably-chosen 

 pairs of stars. In all the pairs the two con- 

 stituents must be separated by nearly the same 

 interval say about 90 and the changes in 

 the distance of each pair are to be measured 

 in the field of an equatorial into which the 

 stars have been reflected by a double mirror, 

 formed by silvering two surfaces of a glass 

 prism. The method is explained at length 

 in several papers printed in the " Comptes 

 Rendus," volumes civ and cv. M. Houzeau 

 claims that in 1871 he suggested the principle 

 upon which this method depends. Sir Howard 

 Grubb has written an elaborate paper on the 

 best forms of instruments for astronomical 

 photography, and has made some experiments 

 with a new object-glass, suggested by Prof. 

 Stokes, which can be changed at pleasure from 

 an ordinary visual objective to a properly cor- 

 rected photographic lens. The change is ef- 

 fected by merely separating the lenses, but for 

 photographic purposes the field of view is 

 rather small. Prof. Abbe has called attention 

 to a heretofore neglected correction in the 

 computation of refraction, arising from the 

 circumstance that the reading of the barometer 

 does not give the true weight of the air until 

 it has been corrected for the variation of 

 gravity due to the latitude of the observer. By 

 applying this correction to the Pulkowa re- 

 fraction-tables, Prof. Abbe finds that at the 

 equator the correction amounts to 0'2" for a 

 zenith distance of 45, and increases with the 

 tangent of the zenith distance. The omission 

 of the correction may, perhaps, explain some 

 of the small systematic differences now exist- 

 ing in star catalogues. Prof. J. M. Schaeberle, 

 of the Ann Arbor Observatory, has recently 

 published a short method of computing refrac- 

 tions for all zenith distances, but his formulae 

 scarcely differ from those given in the Pulkowa 

 refraction-tables. 



Astronomical Photography. Nothing is more 

 remarkable than the way in which the world 

 at large will neglect an important inven- 

 tion or discovery for years, and then suddenly 

 take it up with the wildest enthusiasm. This 

 was well illustrated by the recent electrical 

 craze, during which many persons actually be- 

 lieved that gas-lighting antedated electrical 

 lighting ; and now photography is having its 

 turn. The old bromo-iodized daguerreotype 

 X>lates were not as sensitive as the best wet 

 collodion plates, but they would have borne an 

 long exposure as a modern dry plate, and much 

 of what is now done with gelatine plates might 

 have been accomplished with them. They 

 were inferior to gelatine plates in convenience 

 of working, in extreme sensitiveness, and in 

 the impossibility of printing paper positives 

 from them ; but they were superior in the se- 



