224 CARNEGIE INSTITUTION OF WASHINGTON. 



the discovery by Professor Barnard of a star with an absolute magni- 

 tude of nearly 13.5 provides an opportunity to extend the search for 

 spectral differences to fainter stars. Several other results of this in- 

 vestigation may be referred to briefly. 



1. Abnormal intensity of the hydrogen lines is a characteristic of 

 the highly luminous stars of the K and M types. This is probably 

 related to the so-called giant and dwarf division among the stars. 



2. This division is very clearly shown by a comparison of the num- 

 bers of stars of each absolute magnitude. It may be traced into the 

 stars of the G and F types of spectrum, although it is possible that the 

 selection of the observational material may influence the results to 

 some extent in the case of these two types. 



3. A clear correspondence is shown in the behavior of the lines which 

 varj^ with luminosity in stars when examined in laboratory sources. 

 The absolute-magnitude determinations, accordingly, may be ascribed 

 directly to a physical basis. 



4. High-luminosity stars are characterized by abnormally strong 

 enhanced lines, and fainter stars by strong low-temperature lines. 

 Lines used for absolute-magnitude determinations are included in 

 this more general distinction. 



The measurement and reduction of the photographs of stellar spectra 

 have been carried on by Miss Burwell, Miss Stone, Miss Brayton, and 

 Miss Shumway. In addition to radial- velocity measurements, Miss 

 Burwell has assisted in all of the spectroscopic determinations of 

 absolute magnitude and parallax. 



NEBULAR SPECTROSCOPY. 



A few photographs were obtained by Mr. Pease with the small 

 spectrograph at the primary focus of the 60-inch reflector. An exposure 

 of 85 hours on the Andromeda nebula with the slit set on the minor 

 axis of the nebula, the multiple comparison spectrum device being 

 employed, showed no appreciable rotational velocity. The radial 

 velocity determined by Mr. Adams from this photograph is — 300 km. 



A spectrogram of the star cluster Messier 5, taken under very poor 

 conditions of definition with an exposure time of 53 hours, indicates 

 an F-type spectrum for thjree stars which appear on the plate. 



A photograph of the spectrum of Nova Geminorum obtained in 

 March 1917 shows the spectrum to be essentially identical with that of 

 the previous year. It is of the Wolf-Rayet type and appears to be 

 relatively permanent in character. 



PHYSICAL LABORATORY. 

 BUILDING AND INSTRUMENTS. 



The congested condition of the physical laboratory has been relieved 

 by the construction of an addition by which the floor space was approxi- 

 mately doubled, the new portion having an area of 31 by 44 feet. The 



