266 CARNEGIE INSTITUTION OF WASHINGTON. 



shows that the velocity of light in space is the same for blue and yellow 

 light within one part in a billion. That is, the radiation, which differs 

 in wave-length by approximately a thousand angstroms, differs in 

 velocity by less than one foot a second. 



From a study of the light curves of Novse and variable stars, Mr. 

 Shapley has established with some certainty the existence of a con- 

 tinuous gradation from the so-called typical Nova light-curve, such 

 as that of Nova Aquilse No. 3, to the curves for a certain type of irregu- 

 lar variable star of small variation, similar to those in the Orion Nebula. 

 Spectroscopic results, so far as they go, confirm the relation of the two 

 types, and it is suggested that the cause of variation of Novse and of 

 these variable stars differs in degree rather than in character. Un- 

 published photometric and spectroscopic results from the Harvard 

 College Observatory were of much value in this study. 



The close relationship of the spectra and light curves of Novse and 

 certain variable stars like T Py^idis has been noted by previous ob- 

 servers. 



Mr. Shapley has examined the question of changes in geological 

 climates from the standpoint of recent observations on the move- 

 ment of stars in nebulosity. The peculiar and difficult variables in the 

 Orion Nebula apparently owe their light variations to friction with the 

 surrounding nebulosity, and the prevalence of similar nebulosity 

 throughout the solar neighborhood raises the question of its possible 

 effect in the past on solar radiation and terrestrial temperatures. 



The computational work on eclipsing binaries has been continued by 

 Mrs. Shapley. One of the variables studied, SX Cassiopeise, is of 

 special interest because its mean density is of the order of 0.0005 of 

 the solar density. The variable is, in fact, a very close pair of giant 

 stars, each with a linear diameter comparable with that measured for 

 Arcturus with the interferometer. 



Mr. Shapley and Miss Mayberry have completed an investigation 

 of the 19th magnitude variables of the globular cluster N. G. C. 

 7006 — the faintest and most distant variable stars on record. Seven 

 of the eleven found on the Mount Wilson plates show conspicuous 

 variation in the course of one night, and the other four appear also to 

 be short-period variables. In magnitude and range they are very 

 much alike; and in this cluster, as in M 3,M 5, and other systems, the 

 variables are between one and two magnitudes fainter than the bright- 

 est stars. They are, no doubt, typical short-period Cepheids. 



Preliminary Experiments on Stellar Photometry in the Infra-Red. 



Last summer experiments were begun to determine the possibilities 

 of the new thalofide cells for the measurement of stellar radiation. 

 These cells behave similarly to selenium upon exposure to light, except 

 that their spectral sensitivity lies between 6,000 a and 12,000 a, with a 

 maximum at 10,000a. It was found that cell No. 7 underwent a 



