178 Ri;PORTS OF INVKSTIGATIONS AND PROJElCTS. 



negative, on heavy paper, and the flocculi selected for measurement are cut 

 out and weighed on a delicate balance. Although the areas thus measured 

 are systematically much smaller than those obtained by the photometric 

 method previously employed, the two methods give curves showing the varia- 

 tion in the area, and thus indicating variations in the solar activity, which 

 are very nearly parallel. After a careful comparison, made by measuring a 

 large number of photographs by both methods, the weighing method has 

 been adopted for future work. As it is well adapted for the determination 

 of the areas of prominences photographed at the sun's limb, this additional 

 work is now included in Miss Smith's regular program of measurement. 



The definitive reduction of our photographs of the sun-spot spectrum has 

 been completed by Mr. Adams and Miss Burwell, and the results are now 

 being tabulated for publication. This has involved a very large amount of 

 labor, as it was necessary to measure the wave-lengths and to estimate the 

 intensities of about 11,000 sun-spot lines. The wave-lengths of about 4,900 

 lines in the spectrum of titanium oxide were also measured for comparison 

 with the spot-lines. About 6,300 of the 8,100 unknown lines in the spot- 

 spectrum have been identified with lines of titanium oxide, calcium hydride, 

 and magnesium hydride. In addition to the above work, the separation of 

 the components of many doublets and triplets in the spot-spectrum has been 

 measured. 



Miss Lasby has continued the measurement of plates taken by Mr. Adams 

 for the determination of the solar rotation and the comparison of the spectra 

 of the limb and center of the sun. She has also measured five high-disper- 

 sion photographs of the spectrum of Arcturus. Her work has been facili- 

 tated by the acquisition of a large measuring-machine made by Toepfer, of 

 Potsdam. 



Miss Wickham has measured photographs of the chromosphere spectrum, 

 as well as limb and center plates. She has also devoted much time to the 

 measurement and reduction of laboratory plates taken by Dr. King. 



Miss Waterman has determined the errors of several micrometer-screws, 

 measured photographs of spot-spectra taken for the study of the radial mo- 

 tions discovered by Evershed, and made many least-squares reductions. 



CONSTRUCTION DIVISION. 



The construction division remained under the superintendence of Professor 

 Ritchey until January i. Since that date, apart from observational work on 

 Mount Wilson, he has devoted his time to the work of the optical shop and 

 the designing of the mounting of the lOO-inch reflector. The other work of 

 construction has been done under my general supervision, with Mr. Ayers in 

 immediate charge of the work of the instrument shop, and Mr. Jones in im- 

 mediate charge of the construction work on Mount Wilson. 



