30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



instruments temporarily, though it is also arranged so that certain 

 preliminary work can be done here. Its position, however, immediately 

 south of the main Smithsonian building, is not well suited to refined 

 physical investigations, on account of its proximity to city streets 

 and its lack of seclusion.' 



" The distinct object of astrophysics is, in the case of the sun, for example, not 

 to mark its exact place in the sky, but to find out how it afifects the earth and 

 the wants of man on it; how its heat is distributed, and how it in fact affects 

 not only the seasons and the farmer's crops, but the whole system of living things 

 on the earth, for it has lately been proven that in a physical sense it, and almost 

 it alone, literally first creates and then modifies them in almost every possible 

 way. 



" From the beginning of regular operations at the observatory in 

 June, 1891, till the ist of March, 1892, efforts were chiefly directed 

 to getting the apparatus in satisfactory condition for observations. 

 INIuch time was spent on the improvement of galvanometers, in testing 

 bolometers and prisms, and in the determination of their constants. 



"At length, on March 2, 1892, a ' rehearsal ' occurred, in which 

 the procedure followed in the bolometric investigations of the infra- 

 red solar spectrum at Allegheny, already referred to on a previous 

 page, was gone through with for the first time at the observatory. 

 A second rehearsal occurred on the following day, and on reviewing 

 it an entry was made by the writer March 4, 1892, in the record book 

 in use by Dr. William Hallock, from which the following quotation 

 is taken : 



" I think your yesterday's spectral maps were quite successful for a first 

 attempt — indeed, notably so, and give evidence of the goodness both of the system 

 and of the instrumental means. The salient defect of the latter is in the ' drift ' 

 of the galvanometer, which, though reduced to limits which are insignificant com- 

 pared to those which it had when I first began the study, is still a barrier to the 

 best work. 



"My idea (if drift could be eliminated) would be to have a vertical strip of 

 sensitive paper rolled perpetually upward by a clockwork in the focus of the 

 galvanometer mirror. The sides of this paper are marked in degrees and 

 minutes, corresponding to divisions of the spectrometer circle, whose arm is 

 moved by the same clockwork (through electric or other intermediary), so that 

 when the circle is turned through n minutes of arc, the paper is moved upward 

 linearly by a quantity corresponding to the same angular measure. A light is 

 reflected from the mirror onto the paper, on which are traced the movements of 

 the mirror due to the varying heat of the spectrum and to passing inequalities of 

 the sky transmission. (The mirror movement has to be dampened so that there 

 is no sensible swing.) The whole spectrum could be thus traversed in five 

 minutes or less, as many as twelve curves could be taken in an hour, and a com- 

 posite photograph would eliminate the accidental disturbances. 



