G. Jounstons Stoney on the Penetration of Heat across Layers of Gas. 28 
15. We now come to the very remarkable results which were obtained with 
hydrogen. They are plotted down in fig. 8. A table of some of the results of 
the observations, and the following particulars recorded by De la Provostaye and 
Desains enable us to construct this figure. The loss of heat by radiation from the 
silvered bulb was only +th of the whole amount (presumably at 760 mm. tension). 
The rate of cooling at 20 mm. tension was found to be +3ths of that at 760 mm. 
The rate of cooling at a tension of 12 mm. was rather more than }3ths of that at 
20mm. At 4mm. it fell to about one-half, and, nevertheless, when the rate of 
cooling at this lowest tension was compared with that of a similar bulb placed in 
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conrvectio 
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the open air, it was found to exceed the latter in the proportion of 4 to 3. We 
thus get from the observations* all parts of the figure except those entered in 
dotted lines. The curve representing the loss by convection must lie everywhere 
below the upper line of the figure, and probably lies considerably above the curve 
representing the loss by convection in air. It, therefore, occupies some such 
position as the dotted line of the figure. The shaded interval between this dotted 
line and the upper line of the figure represents the enormous escape of heat to be 
attributed to the penetration of heat through one or two centimetres of hydrogen. 
* The following observations are recorded by De la Provostaye and Desains :— 
Tensions, : .| 760 mm. | 477 mm. 57 mm. 20 mm, 4-4 mm. 
a at m. s. m. s. m. 8. m. m. s. 
Times of cooling, .| 12 46 18 2) 13 40 14 49 2, 24. 
The rates of cooling will be as thé reciprocals of these times, 2.e., as the numbers 652, 625, 610, 562, 
and 304, respectively, and to these numbers the corresponding ordinates of the upper line in our figure 
have been made proportional. 
E 2 
