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XLIII. On the Existence of certain Elements, together ivith 

 the Discover?/ of Platinum, in the Sun. By C. C. 

 Hutchins and E. L. Holden*. 



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 Baltimore, was kindly placed at our disposal by Professor 

 John Trowbridge, under whose supervision and direction the 

 subsequent w^ork 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 systematically prosecuted till somewhat later. 



The grating used is of speculum metal with a ruled surface 

 measuring 6 inches by 2, having 14,438 lines to the inch. 

 It is concave, its radius of curvature being 21J 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 distances 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. 



And here let us parenthetically state that all our wave- 

 lengths are those given by Professor Rowland's photographic 

 map of the solar spectrum, the position of every line referred 

 to being carefully identified upon the map, and its absolute 

 wave-length thus determined. Although some of the nega- 

 tives contain many lines too faint to show on the map, yet 

 we feel confident that our numbers correspond in all cases to 

 those of the map within one tenth of a wave-length. 



The light is brought into the room by means of a porte 

 lumiere, and then sent through the slit after total reflexion 



* From an advance proof from the Proceedings of the American 

 Academy of Arts and Sciences, vol. xxiii. Communicated by Professor 

 J. Trowbridge, of Harvard University, Cambridge, Mass., U.S. 



