Astronomy 27 



variable stars are given from observations made between 1892 and 1905, by Arge- 

 lander's method and with the photometer. The unique feature of the work consists 

 in the application of photometric methods to faint stars near the limit of the Yerkes 

 40-inch refractor. 



No. 138. ADAMS, WALTER S., assisted by JENNIE B. LASBY. An Investigation of 

 the Rotation Period of the Sun by Spectroscopic Methods. Quarto, 

 in+132 pages, 2 plates, 5 text figures. Published 1911. Price $3.00. 

 The results of a determination of the rotation period of the sun from the dis- 

 placements of the spectrum lines. The material employed consists of two series 

 of photographs obtained at the Mount Wilson Solar Observatory during the years 

 1906-7 and 1908 with fixed spectrographs of high dispersive power. The methods 

 of observation and reduction are discussed in full, and a comparison is made with 

 the results of other observers and with the values of the rotation period as derived 

 from studies of sun-spots, faculae, and flocculi. 



No. 93. HALE, GEORGE E., and PHILIP Fox. The Rotation Period of the Sun, as 

 Determined by the Motion of the Calcium Flocculi. Octavo, 54 pages, 

 2 plates, 5 text figures. Published 1908. Price $0.40. 



A series of monochromatic photographs of the sun, made with the spectrohelio- 

 graph of the Kenwood Observatory, in the years 1892-94, provided the material for 

 this investigation. By means of a special measuring instrument the daily motions 

 in longitude of the calcium flocculi in different latitudes were determined. It was 

 found that the law of rotation for these flocculi is almost identical with that for 

 sun-spots. The paper describes the Kenwood spectroheliograph and the globe- 

 measuring instrument, as well as the methods of measurement and the reduction 

 employed. 



No. 235. HALE, GEORGE E. Ten Years' Work of a Mountain Observatory: A Brief 

 Account of the Mount Wilson Solar Observatory. 12mo, 99 pages, 65 

 text figures. Published 1915. Price, in paper cover, 50 cents; in 

 cloth, 75 cents. 



This little book has been written to meet a demand for information regarding the 

 purpose and work of the Mount W'ilson Solar Observatory. As it is intended for 

 the general reader, untechnical language has been used and numerous illustrations 

 have been provided. The purpose of the Observatory is to throw as much light as 

 possible on the evolution of stars and stellar systems. Its researches naturally fall 

 into three chief divisions, comprising: 



(1) Solar observations, for the purpose of adding to our knowledge of the 

 only star open to minute analysis. 



(2) Stellar and nebular observations, bearing directly on the structure of the 

 universe and the physical nature of stars and nebulae. 



(3) Laboratory investigations, for the imitation and interpretation of astro- 

 nomical phenomena. 



The book describes typical methods of work, involving the invention, design, 

 and construction of new telescopes and other instruments, their erection on Mount 

 Wilson in Southern California, their use in photographing celestial phenomena, and 

 the study and interpretation of the photographs in the offices and laboratories in 

 Pasadena. 



No. 115. Boss, LEWIS. Preliminary General Catalogue of 6,188 Stars for the 

 Epoch 1900. Quarto, xxvn+345 pages. Published 1910. Price $7.00. 

 (Out of print.) 



No. 115. Reprint of the above, with corrections to the first edition. Published 

 1915. Price $3.50. 



This volume contains the results of a comprehensive and thorough discussion 

 as to the positions for 1900, proper-motions, and other useful particulars in relation 

 to all stars in both hemispheres that are visible to the naked eye. About 2,000 stars 

 fainter than the sixth magnitude are also included, because they are among the 

 stars which have been most precisely and frequently observed in the past. The 

 primary object of this work was to employ substantially all useful evidence of 



