72 REPORT OF THE SECRETARY. 



B. — PREPARATION FOR PUBLK ATION. 



Owing to the great addition in new matter, and to recent alterations in apparatns 

 and methods, mncli new eopy had to l)e added to the mannseript previously prepared, 

 and all had to be revised. 



Nearly G0,000 comparator measurements of various kinds were reduced throuyrh 

 various stages. Several large scale plots were made and used in connection with the 

 comparison of the dispersion of rock salt and fluorite, and with the determination of 

 wave lengths in the rock salt, fluorite, and glass prismatic spectra. 



Illustrations consisting of holograplis, jjhotographs, plots, and spectrum maps have 

 been gotten ready for reproduction, and the whole has been sent to the engraver. 



f. — MISCKLLA NEOrS 5.T ATTER.S. 



Apparatuit. — Among the several pieces of new apparatus which have been procured 

 are two deserving of special attention. These are the new rock-salt prism "R B U' 

 and the new bolometer case. 



The salt for this prism was obtained from the salt mines of Russia through the 

 efforts and courtesies of officers of both the Russian and United States Governments. 

 The prism was cut and polished l)y Hrashear, and in its final form can not but be a 

 source of great gratification, for with the exception of a few tiny bubbles within, it is 

 clear of flaw or defect of any kind, and forms a great ()0° prism, 15 centimeters on the 

 edge and 17.5 centimeters high, as clear and perfect as the mind could conceive. 



The new bolometer case, in which every accessory of the bolometer but the battery 

 and galvanometer is combined in very moderate compass, required considerable shop- 

 work after its arrival, owing to the carelessness of the maker, but is now in a most 

 satisfactory condition and is a great advance on any previous form. 



Proposed nev gdlvanoineter. — Despite the success of efforts to increase the sensitive- 

 ness of the bolometric apparatus, there still remains much to be desired, for we see 

 and photograph objects by radiations so feeble as to ))e still utterly beyond the 

 powers of even our latest heat-measuring apparatus. Experience suggests the possi- 

 bility that still further advances may be made by increasing the available sensitive- 

 ness of the bolometric ajiparatus. This will be understood when it is said that if our 

 present galvanometer were absolutely free from magnetic and mechanical disturb- 

 ances it could easily l)e made to indicate electric currents six hundred times as small 

 as could now be distinguished with certainty. Designs have been prepared and are 

 already nearly execute<l whereby this great improvement to the galvanometer is 

 hoped to be realized. 



Renovailoa of upparutHK. — The siderostat and otherapparatus were thoroughly over- 

 hauled and renovated late in the year 1891S. 



The new building. — Great want of room has been felt at the Observatory, owing to 

 the introduction of constant-temperature chambers, cooling apparatus, and other 

 bulky impedimenta. The new building of one story andljasement is designed to be 

 used for miscellaneous measurements l)efore crowded out or done with great diffi- 

 culty for lack of room. A very stable i)ier is one of the features of this building. 



Meeting of committee of astronomers and physicists. — Much jjleasure was felt in extend- 

 ing the use of the new library and office room to a committee which drafted the 

 constitution of the American Astronomical and Astrophysical Society, February 8, 

 1899. 



Personnel. — No changes have occurred in the permanent Observatory staff. Mr. 

 C. E. Mendenhall closed his temporary connection with it September 1, 1899. 



CONCLUSION. 



In conclusion it may be said that tlie researches of the present year have well fin- 

 ished our investigation of the infra-red solar spectrum by the accurate determination 



