576 SCIENTIFIC RECORD FOR 1885. 



Photometry of the Pleiades. — "A valuable memoir {Memoires de VAca- 

 demie Imperiale des Sciences de St. Petersbourg, VII serie, tome xxxii, 

 No. G), by Herr Ed. Lindemami,of Pnlkowa, 'Ou the magnitudes of Bes- 

 sel's stars iu the Pleiades,' has recently reached us. A special point of 

 interest lies in the fact that Professors Pickering and Pritchard have like- 

 wise determined the brightness of many of these stars with their respect- 

 ive photometers, each assuming the magnitude of Merope,to which the 

 other stars of the group are referred, as 4-22. Herr Lindemann has also 

 adopted the same magnitude for Meroi)e, which he has used as his stand- 

 ard star. He also employed, as reference stars, Celajuo and Anon. 32, the 

 magnitudes of which he had determined to be 5-27 and 6*ol, respectively. 

 The stars, fifty-two in number, were each observed on two separate 

 nights, only one star of the fifty-three observed by Bessel proving too 

 faint for Herr Lindemann's telescope of five inches aperture. Compar- 

 ing his own results with tliose of Professors Pickering and Pritchard, 

 Herr Lindemann finds, on the whole, a very gratifying agreement; 

 twenty-five stars observed by Professor Pickering showing a mean ex- 

 cess over the Pulkowa observations of 0-04 of a magnitude, and thirty- 

 three stars observed by Professor Pritchard giving a mean excess of 

 0-05. Professor Pritchard's later observations give a yet smaller differ- 

 ence, viz, 0-01 of a magnitude. When it is remembered that the three 

 photometers employed— Herr Lindemann usingaZoelluer photometer — 

 differed entirely in principle, construction, and method of employment, 

 this close agreement would seem to indicate that each may be relied 

 upon with very considerable confidence when the differences of stellar 

 magnitude determined by their means are not very great. The stars 

 Nos. 1, 4, 21, 31, and 33 would appear to be variable, and possibly two 

 others likewise. Pogson's scale has been employed for the conversion 

 of the logarithm of the light of the star into magnitude." {Nature, De- 

 cember 17, 1885.) 



Professor Pickering in the Proceedings of the American Society for Psy- 

 chical Research has tried to find out from the discussion of a large num- 

 ber of observations, whether the knowledge of a catalogue magnitude 

 of a star on the part of a recorder exerts through the medium of " thought- 

 transference " any influence upon the independence of the observers 

 estimate. His conclusion is in the negative. 



ASTRONOMICAL PHOTOGRAPHY. 



Photographic map of the heavens made, with the aid of two objectives, 

 by Paul and Prosper Henry. — "In their first attempts at stellar photo- 

 grai)hy the Messrs. Henry had especially in view the discovery of some 

 rapid means for the construction of their ecliptic charts. As these first 

 attempts gave excellent results, M. Mouchez had apparatus constructed 

 that was especially adapted to stellar photography ; the mechanical 

 I)art is due to Gautier, the optical part being the work of the Messrs. 

 Henry, This new instrument consists of two telescopes in juxtaposi- 



