176 REPORTS ON INVESTIGATIONS AND PROJECTS. 



Spectra of the brightest portion of the Milky Way in Sagittarius. The pho- 

 tographs were secured with exposures of 30 and 65 hours. The spectra 

 appear to be approximately of the solar type, and may have been influenced 

 to some extent by several bright stars of type K present in this region. The 

 work will be continued, guarding so far as possible against this effect, in 

 order to determine whether the A type of spectrum is predominant among 

 the stars forming the Milky Way. 



PHYSICAL, LABORATORY. 



The investigations carried on in the physical laboratory during the year 

 have consisted of further studies of the Zeeman effect for several elements 

 by Mr. King and Mr. Babcock, a determination by Mr. Gale of the displace- 

 ments in the spectra of the arc and spark of the principal lines of iron and 

 titanium at pressures between a partial vacuum and 16 atmospheres, and a 

 study of furnace spectra under pressure by Mr. King. 



The results of the investigation of the Zeeman effect for iron and titanium 

 by Mr. King will be given in detail in Publication 153 of the Carnegie Insti- 

 tution of Washington, now in press. They are summarized briefly in the 

 early part of this report, and are based upon a study of the behavior of over 

 1,100 lines between the limits A 3660 and A 6743. 



Similar studies by Mr. Babcock of the Zeeman effect for chromium and 

 vanadium have been completed and will also be published in detail. Mr. 

 Babcock has carried out a comparison of the curves of frequencies of the 

 occurrence of the magnetic separations for the triplets in the spectra of 

 fourteen elements and has found a close similarity between the positions of 

 maxima and minima. A careful determination of the value of ^A/Aa for the 

 two principal maxima gives for e/m (the ratio of ionic charge to mass) the 

 quantity 1.775, ^ result in almost exact agreement with the mean values 

 obtained by other observers by different methods. Mr. Babcock has made a 

 number of experiments on the production of absorption lines in the magnetic 

 field, in order to imitate more closely the eft'ects observed in sun-spots. 



The study of the Zeeman effect in the laboratory has been carried to a 

 point at which the need of a more powerful field for the separation of very 

 close components and the analysis of highly complex lines is felt greatly. 

 Accordingly, a large electro-magnet of the Weiss pattern has been purchased 

 during the year and is now being erected. This instrument is designed to 

 give a field of about 46,000 gausses with a gap of 2 mm., and is provided 

 with an efficient cooling system admitting of continuous operation during 

 many hours. 



Mr. Gale spent the months of March, April, and May in Pasadena and 

 carried on an investigation of the displacements of the lines in the arc and 

 spark spectra of iron and titanium under pressure. Most previous investi- 

 gations have been made with comparatively high pressures and, accordingly, 



