300 Of the higher regions of the Atmosphere. 
Now, Sir, if large quantities of hydrogen occasionally oc- 
cupy the upper regions of the atmosphere, since its refracting 
power is more than six times that of atmospheric air, (6 61436, 
Biot, Traite de Physique, Tome, 3 page 308,) the rays 
of light must be decomposed on passing into this highly re- 
fracting medium; and thus, I think, the appearances may be 
explaine 
I achasmledge that the facts with which we are acquaint- 
ed, relative to the mixture of gases, are not easily reconciled 
with the remarks of Brisson: but the experiments of Dalton 
and Berthollet on this subject, were made under the common 
seen, the contrary is not stated ; and the gases were confin- 
ed in contact with each other. It would be very interesting 
to perform the same experiments under Cerca pressures 5 
and even in as perfect a vacuum as we can obtain. Even 
granting that extremely small quantities of gas oad be dif- 
fused uniformly throughout the largest vacuum that we could 
produce, I deem it very probable, that if small portions of 
two gases, contained in large exhausted receivers, were made 
to communicate with each other, the mixture would be much 
Jess rapid than when under the pressure of the atmosphere. 
Certainly the mutual repulsion of the particles, which eauses 
_aeriform fluids to diffuse themselves uniformly when external 
pressure is removed, must have some limit. We cannot sup- 
pose that it will exist between the particles at whatever dis- 
tance be removed from each other; but only until) the 
repelling power, which probably exerts itself at comparative- 
ly inconsiderable distances, is balanced by the universal at- 
traction which governs all matter. I do not know of any 
facts which would authorize us to make the same assertion 
respecting the electric fluid ; (which, if there be any, seems 
most likely to form an exception,) = the analogy of nature’s 
works would lead us, even here, to the same conclusion. 
The levity of hydrogen would probaly cause it to ascend 
with great rapidity, ull it arrived at a region where the den- 
sity of the air was equal to its own. It is possible that in 
‘such circumstances, the mixture might not take place with 
_ same —— as at the surface of the earth, and 
hot. at all. 
=e if Mr. Dalton’s hypothesis be true, the 
gas could expand itself with entire freedom, although 
surrounded by air; and therefore would not have a 
