[November., 
728 Cwrespoydetoce. 
heat of a pipe conveying warm water or steam, of a hot-bed, 
&c., is to a great extent retained by a glass covering. Of the 
radiant heat from an Argand lamp 92*3 per cent passes through 
a plate of rock-salt, and 67 per cent through, a plate of flint-glass. 
The higher is the heat of the source of the rays, the larger pro- 
portion is transmitted. — I am, &c., - 
Physicus. 
