Curiosities of Science. 187 



stantly by radiation would then be wholly expended in its 

 liquefaction, on the one hand, so as to leave no radiant surplus ; 

 while, on the other, the actual temperature at its surface would 

 undergo no diminution. 



The great mystery, however, is to conceive how so enor- 

 mous a conflagration (if such it be) can be kept up. Every 

 discovery in chemical science here leaves us completely at a 

 loss, or rather seems to remove further the prospect of probable 

 explanation. If conjecture might be hazarded, we should look 

 rather to the known possibility of an indefinite generation of 

 heat by friction, or to its excitement by the electric discharge, 

 than to any combustion of ponderable fuel, whether solid or 

 gaseous, for the origin of the solar radiation. Outlines* 



DISTINCTIONS OF HEAT. 



Among the curious laws of modern science are those which 

 regulate the transmission of radiant heat through transparent 

 bodies. The heat of our fires is intercepted and detained by 

 screens of glass, and, being so detained, warms them ; while 

 solar heat passes freely through raid produces no such effect. 

 " The more recent researches of Delaroche," says Sir John Her- 

 schel, "however, have shown that this detention is complete 

 only when the temperature of the source of heat is low ; but 

 that as the temperature gets higher a portion of the heat ra- 

 diated acquires a power of penetrating glass, and that the 

 quantity which does so bears continually a larger and larger pro- 

 portion to the whole, as the heat of the radiant body is more 

 intense. This discovery is very important, as it establishes a 

 community of nature between solar and terrestrial heat ; while 

 at the same time it leads us to regard the actual temperature of 

 the sun as far exceeding that of any earthly flame." 



LATENT HEAT. 



This extraordinary principle exists in all bodies, and may 

 be pressed out of them. The blacksmith hammers a nail until 

 it becomes red hot, and from it he lights the match with which 

 he kindles the fire of his forge. The iron has by this process 

 become more dense, and percussion will not again produce in- 

 candescence until the bar has been exposed in fire to a red heat, 

 when it absorbs heat, the particles are restored to their former 

 state, and we can again by hammering develop both heat and 

 light. R. Hunt, F.R.S. 



* Electricity, traversing excessively rarefied air or vapours, gives out light, 

 and doubtless also heat. May not a continual current of electric matter be con- 

 stantly circulating in the sun's immediate neighbourhood, or traversing the 

 planetary spaces, and exerting in the upper regions of its atmosphere those 

 phenomena of which, on however diminutive a scale, we have yet an unequi- 

 vocal manifestation in our Aurora Borealia? 



