Appendix V. 

 REPORT ON THE ASTROPHYSICAL OBSERVATORY. 



Sir : During the past fiscal year there haA'e been no alterations of the obser- 

 vatory buildings beyond slight necessary repairs. Some apparatus for research 

 has been purchased, the usual scientific periodicals have been continued, and a 

 few books of reference have been added to the library. 



The personnel has remained practically unchanged. Miss M. L. Scott served 

 as additional computer from July 5 to August 10, 1907. Mr. J. C. Dwyer, who 

 had served faithfully and with fast growing general usefulness as messenger 

 for several years, died on January 25, 1908. Mr. Meyer Segal was employed as 

 messenger, beginning February 19, 190S, and Mr. L. B. Aldrich as bolometrie 

 assistant from May 11, 1908, to the end of the fiscal year. 



The work of the observatory may be considered under the following heads : 

 1. Publications; 2. Washington observations; 3. Solar eclipse expedition; 4. 

 Mount Wilson observations. 



1. PUBLICATIONS. 



As stated in last year's report, the preparation of Volume II of the annals 

 had been nearly finished before the beginning of the fiscal year. But the com- 

 pletion of the computations, and the revising and rechecking of i-esults contin- 

 ued to occupy the staff until the latter part of Ocober. The revision of proofs 

 continued intermittently until March, and the edition of 1,500 copies was re- 

 ceived in April. About 1,300 copies were at once distributed to libraries, 

 observatories, scientific periodicals, and men of science throughout the world. 

 Commendatory notices by letter and in journals, and requests for copies of the 

 work have been numerous. 



2. WASHINGTON OBSERVATIONS. 



The observation of the relative brightness of different parts of the sun's disc 

 has gone forward as there was opportunity. Improved methods of observing 

 and reducing these observations have been adopted. 



Preparations for observing the absorption of water vapor in long columns of 

 air, for the region of the spectrum where rays are chiefly emitted by the earth, 

 have been carried to such a state that preliminary measurements have been 

 made. Many difficulties attend this research, for the rays observed are wholly 

 invisible to the eye, and are very feeble, even in the emission of the hottest 

 bodies. In sun's rays they are almost wholly absent, because of the absorbing 

 action of the water vapor encountered by the sun's rays in our atmosphere. 

 Few substances are transparent to them, and even rock salt fails in transpar- 

 ency, for some rays are of very long wave-length, which are of considerable 

 importance in the spectrum of the earth. Stray radiation from the walls of 

 the room must be taken into account, and the straying of rays of less wave- 

 length from regions of the spectrum where the emission of hot sources is 

 plentiful is a troublesome difficulty. The investigation is being carried on with 

 a column of moist air about 400 feet in length. The work is under Mr. Fowle's 

 direction. 

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