190 



SCIENCE. 



[N. S. Vol. XII. No. 292. 



special dangers on account of the low alti- 

 tude of the asteroid in the southern hemis- 

 phere. 



W. W. Campbell. The base line which 

 Professor Newcomb has indicated has a 

 great extent, but as to successful working 

 much depends upon a wise compromise 

 which ought to be considered. At the ex- 

 pense of longer observation the observers 

 are going to work near the horizon, where 

 the refraction will be more uncertain. Fur- 

 thermore the image to be measured will 

 not in all cases be satisfactory on account 

 of the vapors rising near the horizon. 

 What amount of difference in the base line 

 will outweigh the differences in the atmos- 

 phere we shall have to compete with ? It 

 appears to me that a base line which gives 

 only two-thirds of the parallax may be more 

 accurate than one which gives five-sixths, 

 in consequence of the better conditions 

 under which the observations may be made. 



G. C. Comstock. We should not be mis- 

 led by the drawing upon the blackboard, 

 because it is not drawn to scale. Taking 

 the indicated positions, we shall not bring 

 ovir observations very near the horizon. I 

 agree that we should not seek the maximum 

 possible base line, there are other consider- 

 ations in the problem, but we should get 

 the longest base line we can without en- 

 croaching upon the horizon, and Pulkowa 

 and Arequipa do not crowd the observations 

 upon the horizon. 



S. J. Brown. We have to take the tele- 

 scopes as they can be found. At Pulkowa 

 they have an excellent telescope, and at 

 Arequipa also ; and they are of identical 

 power. These two stations are fixed, there- 

 fore, by the facts of the case. And so the 

 Cape of Good Hope will be fixed as another 

 station. The photographic program is fixed. 

 I think the matter will be settled according 

 to the circumstances as they exist now. 

 We have three photographic telescopes of 

 13-inch aperture distributed very favorably 



in the southern hemisphere, and three 

 or four in the northern hemisphere. The 

 micrometric problem is one which I think 

 the astronomers of America can agree to 

 co-operate in, and I think we ought to have 

 considerable influence in inducing Strass- 

 burg and Greenwich to co-operate with us. 

 If we can secure the agreement of astron- 

 omers in this country and send word to 

 those in Europe before October 1st, we may 

 possibly save the situation, and perhaps 

 produce results comparable in accuracy 

 with those from the photographic plates. 

 The planet may be observed at Pulkowa 

 and Washing-ton from October 1st to Janu- 

 ary 16th, the observations at Pulkowa ex- 

 tending to an hour angle of 6 or 7 hours. 

 Then the planet would have an altitude of 

 30° ; and the factor can be extended from 

 15" to 30" or even 35". But I have been 

 unwilling to write to foreigners until I 

 could ascertain the opinions of astrono- 

 mers here. 



Winslow Upton. I think if Professor 

 Pickering were here he would assure us 

 that Arequipa is remarkably well situated 

 to adapt it for a southern station. The 

 condition of the climate and the atmosphere 

 is favorable, and it has an elevation of 

 8000 feet above the level of the sea, ensur- 

 ing good definition. Again, the twiUght 

 there is always short. We can be perfectly 

 sure that Professor Pickering will use the 

 facilities of the situation to the utmost. 

 But there is a difficulty from the unknown 

 law of refraction. The discussion of the 

 observations mil take the differential form, 

 but the law is not known at all. These 

 considerations do not apply to Pulkowa, 

 but there the planet will not be low. 



F. L. Chase. With regard to diurnal 

 motion, will it be possible to eliminate the 

 motion of the planet ? 



S. J. Brown. I think the micrometric 

 method in that respect out of the question. 

 The motion of the planet is about 10' in 10 



