198 REPORTS ON INVESTIGATIONS AND PROJECTS. 



what was seen, but no one could accurately delineate the remarkable com- 

 plexity of detail of the features which were visible in moments of greatest 

 steadiness. Some sketches were made in an effort to show these features, 

 but Professor Barnard considered his artistic skill entirely inadequate to the 

 effort. In spite of the immense complexity of detail visible, he was unable 

 to see any trace of the system of fine lines as drawn by Lowell. 



The same freedom from secondary spectrum was especially striking in 

 looking at the stars. The most impressive view Professor Barnard ever 

 had of the Milky Way in a large telescope was with the 60-inch reflector 

 in the principal focus. The stars looked like jewels on black velvet. The 

 sky was rich and dark, and every star was a glowing, living point of light. 



The region of Nova Lacertce (Espin's star) was frequently examined 

 with the focal length of 100 feet. Under good conditions there were a few 

 stars visible which were fainter than Professor Barnard had seen in the 

 40-inch telescope while measuring the stars about the Nova, and the faintest 

 stars he had measured were decidedly more noticeable in the 60-inch. Of 

 course some of this increase of power was due to the greater transparency 

 of the atmosphere at Mount Wilson. 



Given an equal facility for handling the large reflector. Professor Bar- 

 nard would prefer it for visual work on the planets to any of the large 

 refracting telescopes with which he is familiar. 



PROFESSOR HERTZSPRUNG'S INVESTIGATIONS. 



Under a grant from the Prussian Government and the Prussian Academy 

 of Sciences, Prof. Ejnar Hertzsprung, of the Astrophysical Observatory 

 of Potsdam, spent four months (July-October) on Mount Wilson for the 

 purpose of determining the effective wave-lengths of faint stars. The 

 method employed consists in placing a large transmission grating over the 

 end of the tube of the 60-inch reflector, and photographing the very short 

 stellar spectra thus produced. The distance between the first-order images 

 gives the effective wave-length, which serves as a measure of the color of 

 the stars. 



The large grating used in the investigation was made for the 60-inch 

 reflector by Otto Toepfer, of Potsdam. It consists of 273 rubber bands 3 

 mm. in diameter, overspun with black cotton, and separated by spaces of 

 the same width. The grating constant thus being 6 mm. and the focal 

 length about 7,500 mm., the distance to be measured between the two spec- 

 tra of the first order is about i mm. The grating gives excellent results, 

 and a large number of photographs have already been taken. 



The first-order spectra are about three magnitudes fainter than star- 

 images observed without the grating. Photographs of the North Polar 

 Sequence show good measurable spectra of stars down to the fifteenth pho- 

 tographic magnitude, in an exposure of one hour, on Lumiere Sigma plates, 

 with full aperture. 



