PEOFESSOE TTNDALL ON CALOEESCENCE. 17 



rays transmutes them from heat-rays into light-rays. They impinge upon the platinum 

 at a certain rate ; they return from it at a quicker rate. Their refrangibility is thus 

 raised, the invisible being rendered visible. 



To express this transmutation of heat-rays into others of higher refrangibility, I 

 would propose the term calorescence. It harmonizes well with the term " fluorescence" 

 introduced by Professor Stokes, and is also suggestive of the character of the effects 

 to which it is applied. The phrase " transmutation of rays," introduced by Professor 

 Challis*, covers both classes of effiects.- 



§7. 



In the foregoing section I have described arrangements made with a view of avoiding 

 the danger incidental to the use of so inflammable a substance as the bisulphide of 

 carbon. I have since thought of accomplishing this end in a simpler way, and thus 

 facilitating the repetition of the experiments. The following arrangement (Plate I. 

 fig. 6) may be adopted with safety. 



A B C D is an outline of the camera^ 



xy the silvered mirror within it. 



c the carbon points of the electric light.^ 



op the aperture in front of the camera, through which issues the beam reflected by the 

 mirror xy. 



Let the distance of the mirror from the carbon points be such as to render the 

 reflected beam slightly convergent. 



Fill an ordinary glass flask with the solution of iodine, and place the flask in the path 

 of the reflected beam at a safe distance from the lamp. The flask acts as a lens and 

 filter at the same time, the bright rays are intercepted, and the dark ones are power- 

 fully converged. F, Plate I. fig. 6, represents such a fiask ; and at the focus formed a 

 little beyond it combustion and calorescence may be produced. 



The following results have been obtained with a series of flasks of different dimensions, 

 at a distance of 3| feet from the carbon points. 



1. With a spherical flask, 6f inches in diameter: platinum was raised to redness at 

 the focus, and black paper inflamed. 



2. Ordinary Florence flask, 3|- inches in diameter : platinum raised to bright redness 

 over a large irregular space. Near the lamp, the efiects obtained with this flask were 

 very striking. 



3. Small flask, 1-8 inch in diameter, not quite spherical: platinum rendered white- 

 hot ; paper immediately inflamed. 



4. A still smaller flask, 1'5 inch in diameter: effects very good; about the same as 

 the last. 



5. The bulb of a pipette : effects striking, but not quite so brilliant as with the less 

 regularly shaped small flasks. 



* Philosophical Magazine, Ser. 4. vol. xii. p. 521. 

 MDCCCLXVl. D 



