May 2, 1902. J 



SCIENCE. 



(393 



In the evening- session, President 

 Henry S. Pritchett, of the Massachusetts 

 Institute of Technology, spoke on 'The 

 Relation of the American University to 

 Science,' and President Daniel C. Gilman, 

 of the Carnegie Institution, on 'The Ad- 

 vancement of Knowledge by the Aid of the 

 Carnegie Institution.' These addresses 

 were followed by a public reception at the 

 Museum of Science and Art, given in honor 

 of the members of the Society by the De- 

 partment of Archeology of the University 

 of Pennsylvania. 



FRIDAY MORNING SESSION. 



Pkopessoe T. J. J. See, of Washington, 

 in a 'Historical Investigation of the Sup- 

 posed Changes in the Color of Sirius since 

 the Epoch of the Greeks and Romans,' 

 pointed out that the highest authorities of 

 antiquity attributed to Sirius a ruddy 

 color, and that there is no authority who 

 says that the star was white, and that it 

 has become white since the time of the 

 Roman emperors— perhaps since the end 

 of the fourth century. The star may have 

 changed color very suddenly, or its redness 

 may have gradually faded with the cen- 

 turies and disappeared slowly like the an- 

 cient civilization. In modern times the 

 star has always appeared white, and there is 

 therefore no suspicion that the color changes 

 periodically. The redness of a star's light 

 depends, without doubt, mainly upon selec- 

 tive absorption; accordingly, the natural 

 explanation of this change of color would 

 seem to be a change in its atmosphere. 



Professor Ernest W. Brow^n, of Haver- 

 ford, Pa., in a paper on 'Recent Progress 

 in the Lunar Theory,' gave a general ac- 

 count of the lines along which investiga- 

 tion has proceeded during the last thirty 

 years. The work of Dr. G. W. Hill on 

 periodic orbits was the starting point of the 

 investigation undertaken by M. Poincare. 

 The investigations of the latter on diver- 



gent series were also referred to. The sec- 

 ond part of the paper contained an account 

 of the progress made towards verifying the 

 law of the inverse squai'e. The writer also 

 gave an account in some further remarks 

 of the progress made in the theory which 

 he is now working out. He pointed out 

 in what way it might settle some outstand- 

 ing difficulties. 



Professor M. B. Snyder, of Philadel- 

 phia, in a paper 'On a new Method of 

 Transiting Stars,' described a method of 

 driving the ordinary micrometer screw of 

 the transit instrument by means of a small 

 electric motor to the speed pertaining to 

 any given declination, at the same time 

 that the obseiwer by a secondary adjust- 

 ment of the position of the wire secures 

 and maintains bisection of the star, and an 

 automatic record of given positions of the 

 screw is made on a chronograph. The 

 Repsold method of alternately tmrling the 

 screw of a specially constructed microm- 

 eter was held to be radically defective 

 in important particulars. Various devices 

 for accomplishing the electrical method of 

 driving and of regulating the motion of the 

 screw of the transit micrometer, as well as 

 the actual arrangement in use at the 

 Philadelphia Observatory, called for 

 brevity a 'transiter,' were described. The 

 transiter seemed to furnish all the neces- 

 sary facilities of motion and of recording, 

 and not only permitted elimination of all 

 errors excepting that of bisection, but for 

 the first time allowed of the direct deter- 

 mination of absolute personal equation 

 upon the stars themselves at all transits 

 where this might be desired. 



Mr. Percival Lowell, of Flagstaff, 

 Ariz., spoke on 'The Evolution of Martian 

 Topography.' He said that one of the 

 great causes of misapprehension and con- 

 tradictions in former observations of Mars 

 is that the planet looks differently in 

 winter and summer. The dark patches 



