120 REPORT OF THE SECRETARY. 



Inasmuch as the Aid Acting in Charge is also the custodian of the physical 

 apparatus of the Smithsonian Institution, he was concerned in the fitting 

 up of the new instrument room in the south tower of the Smithsonian 

 building, and in the arrangement of the apparatus there. 



A considerable amount of the time of the Junior Assistant was occupied 

 in the preparation of enlarged representations of the holographic results 

 appearing in Volume I of the "Annals " for use by the Secretary in describ- 

 ing these results to various learned societies, and also for exhibition at the 

 Buffalo Exposition. 



(2) Progress of investigations — Adjustment of apparatus. — From my last 

 year's report it will be apparent to how great an extent the Observatory 

 apparatus was removed to North Carolina for use in observing the solar 

 eclipse of May, 1900. It will therefore be understood that no little time 

 was consumed in again setting up and accurately adjusting the apparatus 

 for work here. 



Radiation of the moon. — The first observations made were upon the radi- 

 ation of the moon. These observations, whose general result was given by 

 anticipation in last year's report, in connection with the discussion of the 

 bolometric work on the corona during the eclipse, called renewed attention 

 to the fact, so apparent in your bolometric work at Allegheny, that much 

 the larger proportion of the radiation we receive from the moon is the 

 radiation proper of the lunar soil rather than the direct reflection of solar 

 rays, but that this properly lunar radiation varies exceedingly in amount, 

 depending -on the amount of moisture in our atmosphere. Thus the 

 directly reflected portion of the whole lunar radiation received at the 

 earth's surface may vary from 20 to 40 per cent, according as our air is dry 

 or humid. It may be mentioned that certain similar observations made 

 by the Aid Acting in Charge while upon the eclipse expedition to Sumatra 

 indicated that quite 40 per cent of the lunar rays received in that moist 

 climate are those directly reflected from the sun. 



Tntramercurial plaint*. — Inasmuch as the results of the photographic 

 search for new planets conducted at the eclipse of May, 1900, were fully 

 described in last year's report, it will be unnecessary to refer to them here, 

 more than to say that the comparison and reduction of the eclipse photo- 

 graphs for this purpose really formed part of the work of this present year. 

 It was, however, deemed desirable to again photograph the same region of 

 sky with the lens employed at that eclipse, and apparatus was set up and 

 used for this purpose in January of the present year; but satisfactory 

 results had not been obtained when it became necessary to send the appa- 

 ratus to Sumatra. 



Galvanometer. — The sensitive galvanometer mentioned in my last year's 

 report, and from which the greatest usefulness is expected, has absorbed 

 considerable attention; anil although progress has not, owing to other 

 occupations, as yet passed beyond an experimental stage, it is yet so satis- 

 factory as to deserve a preliminary notice. By way of introduction atten- 

 tion is drawn to the distinction between the computed sensitiveness of a 

 galvanometer and its actual or working sensitiveness. In the older prac- 

 tice of perhaps twenty years ago the most sensitive galvanometers had 

 needle systems of several hundred milligrams weight, and they were, 

 owing to their great inertia, customarily used with a time of single swing 



