180 On the Reflexion of Light by Incandescent Surfaces. 



A beam of ligbt polarized by reflexion at the proper angle 

 from a plate of glass, was made to fall on the platinum surface, and 

 then analysed by a tourmaline ; no difference was perceptible in 

 the plane of polarization, whether the platinum was ignited or 

 not. 



The light reflected from the platinum was similarly polarized 

 and analysed ; but no diff'erence dependent upon incandescence 

 was detected. 



A wire of platinum, 6 inches long and ^'^ th of an inch in diame- 

 ter, was vertically suspended in the narrow Assure of the shutter ; 

 the bands of interference were received on paper placed at differ- 

 ent distances from the wire, and examined both by the eye and 

 by a lens ; no difference could be detected in these bands when the 

 wire was ignited by a voltaic battrey. 



In all the above experiments the foil or wire was ignited by 

 the battery previously to the commencement of each class of 

 experiment, so as to avoid any effect arising from the alterations 

 caused by the platinum having been subjected to heat, — such, 

 for instance, as the effect of annealing might produce, or the 

 burning off from it of films of moisture, or of oxidable sub- 

 stances. 



The general result of these experiments is, that no difference 

 is perceptible by the eye in light reflected by a polished surface, 

 whether that surface is ignited or not ; that the superficial mo- 

 lecular uniformity which causes a bundle of parallel rays to 

 preserve their parallelism of direction when reflected, is, if the 

 ignited substance be inoxidable, not broken up by ignition. 



I know of no photometer which would be suitable for indicating 

 their effects with greater accuracy than the eye ; but, although 

 these results lead to a conclusion different, I believe, from that 

 which would have been arrived at a priori, they by no means 

 exclude the possibility or even probability of some difference being 

 produced in the direction or character of light reflected from 

 ignited surfaces as compared with that reflected from unignited 

 surfaces. 



The fixed lines in the spectrum, for instance, differ materially 

 according to the source of light ; and even supposing the ignited 

 surface to make no difference in the character or position of 

 the fixed lines of reflected solar light, a point which I have no 

 apparatus sufficiently delicate to detect, yet there is every pro- 

 bability of novel and valuable results being attained by the inter- 

 ference of this light of incandescence with that of solar or other 

 light reflected from the incandescent body, the same body being 

 then in some sense the source of two different descriptions of 

 light, which differences arc capable of detection by the different 

 position and characterof the fixed lines in their respective spectra. 



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