ON THE SUN'S HEAT. 399 



through a globe of homogeneous gas left to itself 

 in space, and losing heat by radiation outwards 

 so slowly that the heat-carrying currents produce 

 but little disturbance from the globular form. 



One very remarkable and important result which 

 he finds is, that the density at the centre is about 

 twenty l times the mean density ; and this, whether 

 the mass be large or small, and whether of oxygen, 

 nitrogen, or hydrogen, or other substance ; pro- 

 vided only it be of one kind of gas throughout, 

 and that the density in the central parts is not 

 too great to allow the condensation to take place, 

 according to the ordinary gaseous law of density, 

 in simple proportion to pressure for the same 

 temperatures. We know this law to hold with 

 somewhat close accuracy for common air, and for 

 each of its two chief constituents, oxygen and 

 nitrogen, separately, and for hydrogen, to densities 

 of about two hundred times their densities at our 

 ordinary atmospheric pressure. But when the 

 compressing force is sufficiently increased, they 



1 Working out Lane's problem .independently, I find 22j as very 

 nearly the exact number. 



