October 7, 1898.] 



SCIENCE. 



451 



instrument, the axis being more inclined 

 to the plane of the equator for one observer 

 than for another ; (4) the apparent rate of 

 clock during the evening, due probably to 

 increasing fatigue; (5) that due to magni- 

 tude of stars. Professor Searle pointed out 

 a collimation effect on transits due to bad 

 focus of eyepiece, the lines being displaced 

 by reflected light in illumination. This 

 was shown optically and by a series of 

 transits by two observers, Professor Searle 

 and his assistant, Mr. J. A. Dunne, using 

 different foci of eyepiece. 



In the discussion Professor W. H. Picker- 

 ing suggested that the doubling of wires 

 noticed in the transit instrument under 

 false focusing was analagous to the doubling 

 of the lines of Mars, and that the latter 

 phenomenon was probably due to false 

 focus, and hence doubling of the image in 

 the human eye. Professor Comstock stated 

 that there is a law of variation of personal 

 equation with the declination, but that 

 there is also a variation due to physical 

 condition. When the observer is tired, ob- 

 servations are made more quickly. Profes- 

 sor Eastman said that he had found that 

 malarial fever brought down the personal 

 equation as much as half a second earlier 

 and that there was also a diurnal variation 

 in the personal equation. Mr. Hayford 

 stated that the experience of the United 

 States Coast Survey indicated that personal 

 equation was not appreciably affected by 

 using different forms of signal keys. 



Professor George C. Comstock presented 

 ' Some Investigations Eelating to Zenith 

 Telescope Latitudes.' In the course of a 

 determination of the constant of aberration 

 it was found that two causes of error 

 entered. In the first place, it was noted 

 that any local temperature changes of the 

 atmosphere unsymmetrical with respect to 

 the instrument had a very serious influence 

 on the apparent variation of the latitude. 

 In the second place, general variation in the 



atmospheric refraction was no t eliminated 

 The atmospheric layers are not normal to 

 the vertical, and the barometric and ther- 

 mometric gradients vary irregularly. The 

 zenith telescope gave a constant of aberra- 

 tion varying from 20". 38 to 20". 64, with a 

 range of 0".26, while even the carefully de- 

 termined values of Preston, 20". 43, and 

 Gill, 20". 58, gave a range of 0".15. At 

 least a partial explanation of these varia- 

 tions may be found in the local conditions 

 surrounding the various observatories. 

 Comparing the values derived at ISTew York, 

 20".46, with that of Naples, 20".53, the dif- 

 ference is found to be such as may be ac- 

 counted for by the diurnal temperature 

 changes accompanying the changing land 

 and sea breezes of the respective places. 

 The large value, 20". 58, obtained at the 

 Cape of Good Hope by Gill is capable of 

 similar explanation, and no case has been 

 found that violates this hypothesis. The 

 result is that the local conditions of every 

 place affect the determination of the aber- 

 ration constant, and in such investigations 

 it becomes advisable to abandon the zenith 

 telescope and all other instruments which 

 depend upon the vertical as a reference line. 



Professor Doolittle stated that he had 

 called attention to the outstanding varia- 

 tions in latitude determinations and believed 

 the cause to be a variation in the refraction. 

 The deviation is a good many times as 

 great as the probable error of the observa- 

 tions. The limit of accuracy of the zenith 

 telescope method has been reached. 



Doctor Harold Jacoby presented a paper 

 on ' Photographic Eesearches near the Pole 

 of the Heavens.' The object of the research 

 is to furnish new values of the fundamental 

 constants of stellar astronomy. The plan 

 consists in making exposures for short 

 trails around the pole, like those first 

 made at the Harvard College Observatory. 

 The records on the plates being made apart 

 from either clock or graduated circle fur- 



