FROM THE HIGHER ATMOSPHERE. 467 



In the paper now submitted to the Society, it will be hence 

 expedient to take a retrospect of the facts which have been 

 disclosed relative to the communication of heat. In framing 

 this abstract, I shall abstain from all hypotheses, which might 

 assist, only to deceive, the imagination, but content myself with 

 stating the facts really ascertained, and with tracing out the 

 consequences to which they distinctly lead. 



I have observed, that Heat never appears in a detached 

 form. Yet its materiality is evinced, by the expansion which 

 it invariably communicates to the substances with which it 

 unites. While it is attracted by any bodies, therefore, it must 

 introduce into them some repulsive force, which had previously 

 existed among its own particles. Heat must hence be a fluid 

 of extreme tenuity, yet endued with an irresistible elastic 

 force. But when a, substance, either from a chemical or me- 

 chanical impression, suffers a sudden change of constitution, 

 and makes a copious discharge of heat, this emission is al- 

 ways accompanied by an effulgent light. On the other hand, 

 when the rays of the sun, or even those of a bright lamp, 

 are intercepted by any body, and seem lost or extinguished, 

 a corresponding increase of warmth is immediately betrayed 

 at the absorbing surface. It follows from this and similar 

 facts, that heat is the same fluid as light, only in a state of rest 

 and combination. In short, heat is latent, invisible, light, — 

 the a.<puvjov <p&>g of the ancients, — which has been arrested in its 

 rapid flight, and cannot again be liberated, without such a 

 violent change of condition, as will leave entire the repulsion 

 of its own particles, to create the requisite projectile force. 

 In ordinary cases, however, the light remains imprisoned in 

 the substance with which it combines, and only migrates from 

 one portion to another. 



3 N 2 The 



