694 



SCIENCE. 



[N: S. Vol,. XV. No. 383. 



were called seas, but it has been found that 

 there are no seas on Mars. There are no 

 large bodies of water, and the question is : 

 Are there even small ones? The surface 

 is vastly different from that of the earth, 

 in that it is apparently all land, but there 

 is a sstrange similarity in the air currents. 



He described the investigations of 

 Schiaparelli and others and deduced evi- 

 dence that the so-called canals are vegeta- 

 tion. 



Mars is passing, like the earth and the 

 moon, through a process of drying up. It 

 is not as far advanced as the moon, where 

 there is no moisture or atmosphere, but 

 it is farther advanced than we are. 



Professor Chas. L. Doolittle, of Phil- 

 adelphia, presented a paper on 'Results of 

 Observations with the Zenith Telescope at 

 the Sayre Observatory.' In 1876 was be- 

 gun at the observatory erected by Robert 

 H. Sayre at South Bethlehem, Pa., a series 

 of 'Latitude Observations' which was con- 

 tinued with considerable interruptions un- 

 til August 19, 1895. The final results of 

 the latter part of this series, from January 

 19, 1894, till the close, were published in 

 full about one year ago. 



The present communication, which con- 

 cerns the earlier portion of this work, com- 

 prised three sections or subdivisions. 



1. Investigation of the right ascensions 

 and declinations of the stars employed in 

 the latitude work— 254 in all. 



2. Results of latitude observation from 

 1876 to 1891—2,623 determinations. 



3. Results of observations from October 

 10, 1892, to December 27, 1893—2,900 de- 

 terminations. 



In section 2 the latitude determinations 

 discussed are distributed very unequally 

 through the years 1876, '77, '78, '85, '86, 

 '88, '89 and '90. With the exception of 

 those of 1889-90, they are not well adapted 

 to an investigation of the periodic changes 

 of the latitude. 



The investigation of the constant of 

 aberrations was contemplated in planning 

 the work of 1889-90 and that of 1892-93, 

 though it w^as at that time regarded as a 

 kind of by-product. Each observation 

 furnishes one equation for this purpose. 

 The 2,900 equations of the latter series 

 were combined by a process of 'bunching' 

 to form 190 separate- equations, which were 

 solved in the usual way, giving for the 

 aberration constant the final value 



20."551±.009. 



A peculiar feature of the latitude values 

 is a progressive diminution of the mean 

 value. 



Thus we have the following mean results : 



1876-78 Latitude =40° 

 1889-90 40° 



1892-93 40° 



36' 23'.81" 

 36' 23.41" 

 36' 23.11" 



No satisfactory explanation of tliis ap- 

 parent diminution has been found. 



Professor John Trowbridge, of Cam- 

 bridge, presented an interesting paper on 

 the 'Spectra of Gases at High Tempera- 

 ture,' which was illustrated by a series of 

 lantern slides. He called attention to his 

 discovery of dark lines in the spectra of 

 gases not due to absorption, which do not 

 change the silver salt and which give 

 therefore bright lines on the negative. 

 This shows that there are rates of vibration 

 to which the photographic plate does not 

 respond. Tliis discovery leads us to be- 

 lieve that the solar spectrum is probably 

 far more complex even than we have sup- 

 posed. 



AFTERNOON SESSION. 



Professor A. Stanley Mackenzie, of 

 Bryn Mawr, presented a paper, entitled, ' On 

 Some Equations Pertaining to the Prop- 

 pagation of Heat in an Infinite Medium,' 

 in which attention was called to the neces- 

 sity of trying to interpret in tenns of phys- 

 ical conceptions all the mathematical 



