14 PROCEEDINGS OP THE AMERICAN ACADEMY 



Investigations on Light and Heat, made and published wholly oe in paet with 

 Appkopeiation from the Rumford Fund. 



III. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 

 HARVARD UNIVERSITY. 



ON THE EXISTENCE OF CERTAIN ELEMENTS, 



TOGETHER WITH THE DISCOVERY OF 



PLATINUM, IN THE SUN. 



By C. C. Hutchins and E. L. Holden. 



Presented by Professor John Trowbridge, March 9, 1887. 



Late in the fall of 1886 it was decided by the writers, who were then 

 at work in the Physical Laboratory of Harvard University, to attempt 

 a revision of some of the previous work in regard to the chemical 

 constitution of the sun, as well as to discover, if possible, new facts 

 bearing on the same subject. For the purpose of this investigation 

 a magnificent diffraction grating, made by Professor Rowland of Bal- 

 timore, was kindly placed at our disposal by Professor John Trow- 

 bridge, under whose supervision and direction the subsequent work has 

 been done. 



After some delay caused by the mounting of the grating and its 

 attachments, work was begun early in January, 1887, but, owing to 

 bad weather and other hindrances, was not regularly and systemati- 

 cally prosecuted till somewhat later. 



The grating used is of speculum metal with a ruled surface meas- 

 uring 6 inches by 2, having 14,438 lines to the inch. It is concave, 

 its radius of curvature being 21^ feet, and is mounted according to 

 Professor Rowland's method. Suffice it to say, that the method is 

 such that, by simply rolling the camera along an iron track, it passes 

 not only from one part of the spectrum to another, but also to the 

 spectra of different orders, at the will of the operator. As the dis- 

 tances on this track are proportional to the relative wave-lengths of 

 the lines that fall successively on a given point in the camera, it is 

 easy, by means of a suitable scale of equal parts placed beside the 

 track, to set the centre of the photographic plate instantly within a 

 single wave-length of any given line in the spectrum. 



