178 Mr. W. R. Grove on the Reflexion and 



publish them, aud can only guess that it was in accordance with 

 my general habit of not publishing negative results. The results 

 here, however, though negative, seem to me interesting, as posi- 

 tive results would a priori be expected ; and if you think them 

 worth publishing in the Philosophical Magazine they are at 

 youi" service. 



Yours faithfully, 



W. R. Grove. 



The difference in appearance to an observer of a polished sur- 

 face when at ordinary temperatures and when ignited, is suffi- 

 ciently marked. The self-luminous character of the ignited 

 body apparently removes the impressions of surrounding objects, 

 aud would lead to the belief that reflexion, at least that of the 

 character yielded by polished surfaces, was destroyed. Such 

 has been the a priori impression of those whose opinions I have 

 asked on the subject. My own belief was, that if polished sur- 

 faces when ignited reflected light, they at all events broke up or 

 scattei'ed the reflected rays, and would cease to have the character 

 of a polished surface ; and that if they reflected light at all or 

 notably, they would reflect it as paper or snow does, dispersing 

 the i-ays so as to produce a general impression of luminosity, 

 instead of throwing them back in a parallel beam, or one in which 

 they preserved their original relative inclination. 



The subject appeared worth investigation ; and as I could not 

 find that it had been attempted, I determined to make a few 

 experiments upon it. The difficulty which immediately presented 

 itself was, that the surfaces which are mainly employed for po- 

 lished reflexion being oxidable metals, their physical structure 

 would be changed by the oxidation consequent on incandescence. 

 Gold or platinum, therefore, were the only substances which 

 promised any success ; and the latter, from its reflecting white 

 light and more ready capability of retaining a high temperature, 

 was selected. A strip of platinum-foil, 2 inches long by 0*2 

 broad, was firmly stretched on a piece of plate glass, polished 

 with putty powder and tripoli until it had reached as high a 

 lustre as it could be made to attain. One extremity was then 

 fixed in a clamp attached to a wooden frame ; and to the other 

 extremity was attached, by a similar clamp, a metal Aveight, from 

 which weight a wire extended and dipped into a vessel of mer- 

 cury : the whole was arranged with care, so as not to bend or 

 disturb the plane surface of the platinum. The foil thus sus- 

 pended was brought opposite a vertical cleft in a window-shutter 

 facing the meridian, which cleft could be made of any convenient 

 size by horizontally moveable boards. The platinum-foil was 

 placed opposite the cleft, so as to receive a sunbeam ; a sheet of 



