454 



SCIENCE. 



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



ing two stars on same plate. Dr. George 

 E. Hale stated that a machine, intended 

 'to rule gratings 9 inches by 15 inches, 

 was now being built at the Yerkes Obser- 

 vatory. The great difi&culties attending 

 ruling of surfaces of sharp curvature were 

 described by Dr. Poor. 



In discussing the methods of producing 

 normal spectra of stars, Mr. Edward S. 

 King stated that at the Harvard College 

 Observatory two methods of transforming 

 the prismatic into the normal spectrum had 

 been tried with success. In the first, pho- 

 tographs were taken of the original plate 

 through a slit with the plates moving at 

 differential rates. In the second method 

 the plates are inclined to the axis of the 

 lens, so as to make the scale exact for three 

 points of it while maintaining good focus. 

 The first method is applicable for produc- 

 ing any unequal change of scale. The 

 second, though of an approximate char- 

 acter, is the better working method, Mr. 

 King showed admirable photographic com- 

 parisons of star spectra with Rowland's 

 map. 



Professor E. C Pickering added that the 

 method just described was thoroughly 

 general and that all scales were thus re- 

 producable. He believed that the Orion 

 lines could be well investigated by a grat- 

 ing, as suggested by Dr. Poor. 



Professor G. W. Hough discussed 'The 

 Effect of Atmospheric Disturbance on Tele- 

 scopic Definition.' The local atmospheric 

 disturbances should be differentiated from 

 the general atmospheric conditions. As 

 the object-glass of the largest telescope is 

 infinitely small compared to the size of the 

 atmospheric waves the disturbance will 

 vary directly with the magnifying power. 

 When a disturbance is just in front of the 

 instrument there is displacement and dis- 

 tortion as well. Capping the object-glass 

 usually produces no improvement. 



Professor "W. H. Pickering said the local 



conditions at Arequipa are satisfactory. 

 Caps make little difference with large 

 telescope, but with 6-inch telescope, or less, 

 caps are valuable. Double stars are not 

 the best test of seeing, but rather detail 

 work on planets. Professor Hale said 

 small telescopes are not as good in fair see- 

 ing as big ones for any work. There are 

 many false statements on this point. The 

 two faults of seeing are jumping and blurs. 

 At Flagstaff there is a lively jumping. The 

 highest power used at Yerkes is from 2,500 

 to 3,000. 



Miss Agnes M. Clerke's paper ' On the 

 Spectra on Certain Nebulae,' read in the au- 

 thor's absence by Professor Snyder, called 

 attention to the demand for a special study 

 of the spectra of white nebulae, by reason of 

 the nature of their structure, their mode of 

 distribution in the heavens, and the quality 

 of their light differentiating them from the 

 gaseous nebulae. Miss Gierke proposed 30 

 Doradtis, whose spectrum Professor E. C. 

 Pickering had described as ' partly stellar 

 and partly gaseous;' Messier 1, of which 

 Pierce and Winlock, and later Campbell, had 

 made interesting observations, and l!^. G. C. 

 6299 as examples of this anomalous class. 

 Professor E. C. Pickering, exhibited several 

 recent photographs of spectra of the nebulae 

 indicated by Miss Gierke. 



Mr. J. F. Hayford, in speaking of a 

 ' Proposed Publication of the Coast and 

 Geodetic Survey,' said that the Coast and 

 Geodetic Survey proposes to publish in the 

 form of a catalogue of north polar distances 

 the computed data which it now has in its 

 possession. The catalogue will comprise 

 stars which have been observed for latitude 

 in the survey. The number of stars, 6th 

 magnitude and brighter, comprised in the 

 catalogue will be about 3,500. The degree 

 of accuracy pertaining to each polar dis- 

 tance and proper motion will be indicated 

 by attached probable errors. The system- 

 atic corrections and weights assigned in 



