143 
screens of extreme tenuity by radiant heat. 
face, the effect diminishes rapidly with every remove of the 
screen from the heated body.* This fact which he has 
established both by experiment and reasoning, is an infallible 
test for the opacity or transparency of all kinds of screens. 
Hence in the preceding experiment, the effect was not pro- 
duced by heat radiating from the posterior surface of the 
screen, but by heat actually radiating through the screen in 
the same manner as light radiates through water, or other 
transparent fluids. 
* Leslie’s Inquiry, page 74. 
