452 



SCIENCE. 



[N. S. Vol. VIII. No. 197. 



nish an independent method. The partic- 

 ular negatives used were made at Helsing- 

 fors by Professor Anders Donner, and the 

 northerly latitude reduces distortion occa- 

 sioned by refraction to a minimum. For- 

 mula suitable for the complete reduction of 

 ordinary polar plates star photographs as 

 well as for the special plates described have 

 been deduced and an application made to 

 measures on one plate of six images of each 

 of ten stars, with encouraging results. A 

 discussion was undertaken, assuming first 

 that the instrument remained fixed during 

 the exposure, and second that it was in 

 motion. Making the reductions according 

 to the latter hypothesis the results are in 

 accord with the best north polar distance 

 determinations of Auwers. The line of 

 motion was vertical, by sagging. All the 

 images on two Helsingfors plates, made six 

 months apart, will be measured and the re- 

 sults treated for a general test of the possi- 

 bilities of the method. The work already 

 accomplished will soon be published in full 

 detail. 



Professor Pickering said that aberration 

 and nutation could be thus best determined, 

 and that the 15-inch Draper telescope has 

 for several years beea photographing the 

 pole every clear night with automatic ex- 

 posure, the plate in some cases hanging ver- 

 tical so as to eliminate one equation of con- 

 dition . Professor Paul held that lateral and 

 vertical refraction might enter as disturb- 

 ing factors. Professor Comstook, while 

 agreeing with Professor Paul as to the pos- 

 sibility of refraction variations, held it to be 

 highly desirable that Doctor Jacoby should 

 prosecute his researches. Doctor Jacoby 

 remarked that a new method like this should 

 be received with scepticism and that the test 

 of this plan would be by thorough work 

 extending perhaps over one generation. 



Mrs. M. Fleming's paper on the ' Stars of 

 the 5th Type in the Magellanic Clouds ' 

 was presented by Professor E. C. Pickering. 



Stars having spectra consisting mainly of 

 bright lines belong to Type V. In 1891 

 the number of these stars known was thirty- 

 three. Three of these were discovered by 

 Wolff and Eayet, one by Respighi, six by 

 Copeland, three by Pickering and twenty 

 from the Draper Memorial Photographs of 

 the Harvard College Observatory. In May, 

 1897, the number known was sixty-seven. 

 All of these stars lie closely along the cen- 

 tral line of the Milky Way, and, although 

 the sky had been equally well covered with 

 spectrum plates from pole to pole, a careful 

 examination of the plates failed to show any 

 of these stars outside of this region. 



On May 2G, 1897, an examination of two 

 photographs taken at Arequipa with the 

 Bruce telescope showed a group of six of 

 these objects in the Large Magellanic Cloud. 

 Two later plates add fifteen more, and these 

 with three other stars in the Milky Way, 

 and one in the Small Magellanic Cloud, 

 make the total number of these stars, so 

 far known, ninety-two. Thirteen of these 

 were found visually ; all the others have 

 been found by Mrs. Fleming from Draper 

 Memorial photographs. The great advan- 

 tages of photography in the study of stellar 

 spectra is thus again demonstrated. 



The presence of so many stars of the 

 Fifth Type in the Magellanic Cloud estab- 

 lishes another connection between this ob- 

 ject and the Milky Way. 



Professor Solon I. Bailey presented a 

 paper on ' Variable Stars in Clusters.' A 

 systematic examination of twenty of the 

 most interesting, dense, globular clusters has 

 been made. In these clusters 18,600 stars 

 were compared, of which 501 were found to 

 be variable. In only a few of these clusters 

 does the percentage of variables amount to 

 more than one per cent., and in many cases 

 it is less. A few clusters, however, give 

 remarkable results. The most striking is 

 Messier 3, where 132 stars out of a total of 

 900 are variable, or one in seven. Other 



