22 G. Jonnstone Sronzy on the Penetration of Heat across Layers of Gas. 
necessarily very imperfect, lends support, so far as it goes, to the conclusion that 
the apparently anomalous escape of heat which De la Provostaye and Desains 
investigated was due to penetration. 
14. Hitherto I have used only the observations recorded in a memoir published 
in the Comptes Rendus, vol. xx. (1845), p. 1767. In asecond memoir published in 
the Comptes Rendus, vol. xxii. (1846), p. 77, Dela Provostaye and Desains record 
observations made with a silvered thermometer within a blackened cylinder, which 
appears to have been of the same size as that used in the former investigation, and 
which they charged successively with hydrogen, carbonic anhydride, protoxide of 
nitrogen, and a mixture of air and hydrogen. 
In carbonic anhydride the results of ex- 
periment are represented by fig. 7.* In 
this gas the total rate of cooling increased 
when the tension was diminished from 12 to 
4 mm. This observation took De la 
Provostaye and Desains so much by surprise 
that they repeated and varied their experi- 
ments, till they were fully satisfied that the 
existence of the increased escape of heat was 
proved. 
With protoxide of nitrogen (N,O), a gas which has the same specific gravity as 
carbonic anhydride, their observations gave similar results. Between tensions of 
35 mm. and 12 mm. the total rate of cooling remained nearly constant, and, as in 
carbonic anhydride, it was slightly increased by further diminishing the tension 
from 12 down to 4mm. This slight increase was. less in the protoxide of nitrogen 
than in the carbonic anhydride: about 51,th of the whole amount in the former 
gas, about th in the latter. 
The observations with these gases show that the form of the curve represented 
in fig. 5 is in an appreciable degree different in different gases, and that there are 
some gases in which the increase of the escape of heat by penetration when the 
tension is decreased will, within certain limits of temperature, exceed the decrease 
of the escape of heat by convection. 
* De la Provostaye and Desains record the following observations, from which the curve in the text has 
been plotted down, the ordinates being drawn proportional to the reciprocals of the observed times of 
cooling :— : 
Tensions, . | 35 mm. ~ | 12 mm. | 4 mm. 
| m. s. m. s. m. s. 
Times, . ; Ig) 4 19 38 WS) 
The reciprocals are proportional to 282, 283, and 309. The thick line in fig. 7 is not quite correctly 
drawn : it should have been almost horizontal between 12 to 35 mm. 
