730 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



ble depths than at the surface, aud assuming that while convection 

 is going on, the temperature must be the same at all depths, draws 

 the conclusion that gravity, instead of internal heat, must be the 

 cause of this increase of temperature. It is hardly necessarj^ to 

 remark that uniformity of temperature is the ultimate result, and not 

 the attendant of convection, which canuot take place except when 

 the heat is in excess below, and ceases as soon as uniformity is re- 

 stored. Some of the ideas in regard to force which were advanced, 

 are remarkable, to say the least, and the conclusion arrived at, that 

 "the true cause why the earth is not drawn into the sun, as well 

 as why two molecules do uot touch, i? not the centrifugal force, 

 but the force of heat," will, I think, rather surprise those who 

 are familiar with the principles of mechanics. 



A transposition in this statement of the cause and effect, would, 

 in my opinion, make it more probably correct. In other words, 

 it is not improbable that heat is simply the momentum or centri- 

 fuo-al force of atoms revolving about each other in orbits. I pro- 

 pose, in a future paper, to suggest a possible way in which this 

 may take place, and to exhibit some models in illustration. 



An attempt has been made to reconcile the apparent conflict 

 ■which exists between the phenomena of gravitation and the law 

 of conservation of force, by supposing force to exist in a latent 

 or "potential" form as well as in an active state, so that in the 

 case of gravity the amount of its force is measured, not by its 

 intensity at any particular point, but by the entire effect, which it 

 is capable of producing. This accounts for the disappearance of 

 the force which takes place only by giving the last force a name, 

 and it appears to me, moreover, to complicate unnecessarily our 

 ideas of the nature of force. The simplest way to define force is 

 to call it "that which, in becoming associated with matter, pro- 

 duces motion or change of motion." In a paper published in 

 Silliman's Journal for September, 1865, I have shown that an 

 external aud universal force might produce gravitation without 

 undergoing any variation in quantity. 



I consider the nebular hypothesis to have undergone mathe- 

 matical demonstration. It explains a very great number of facts 

 of which no attempt has been made at exphnnation in any other 

 way, and not one fact is in conflict with it. The apparent varia- 

 tion in some of the outermost planets and their satellites occurs 

 where irregularities would naturally be expected, and are among 

 those exceptions which, confirm the rule. 



