Prof. Tyndall on Calorescence. 443 



mingled with them; they were exclusively extra-red. The action 

 of the atoms of platinum, copper, silver, and carbon upon these 

 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 in- 

 visible 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 

 effects. 



§ 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 follow- 

 ing arrangement (Plate IV. fig. 6) may be adopted with safety. 



ABCJ) 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 

 powerfully converged. F, Plate IV. fig. 6, represents such a flask ; 

 and at the focus formed a little beyond it combustion and calo- 

 rescence may be produced. 



The following results have been obtained with a series of flasks 

 of different dimensions, at a distance of 3J feet from the carbon- 

 points. 



1. With a spherical flask, 6j 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 effects obtained with this flask were very striking. 



3. Small flask, 1*8 inch in diameter, not quite spherical: 

 platinum rendered white-hot j paper immediately inflamed. 



4. A still smaller flask, 1-5 inch in diameter: effects very 

 good ; about the same as the last. 



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



