PROFESSOR LOVERING'S ADDRESS. 319 



axioms of mechanics having free range only in astronomy, where fric- 

 tion, resistance, and collision, do not interfere. The conservation of 

 energy, in its extended signification, promises to he, like its forerun- 

 ners, a valuahle guide to discovery, especially in the dark places into 

 which physical science has now penetrated. The caution which La- 

 grange has given in reference to similar mechanical principles, such as 

 the conservation of the motion of the centre of gravity, the conserva- 

 tion of moments of rotation, the preservation of areas, and the prin- 

 ciple of least action, is not without its applicability to the new gener- 

 alization. Lagrange accepts them all as results of the known laws of 

 mechanics, and not as the essence of the laws of Natui'e. The most 

 that physical science can assert is, that it possesses no evidence of the 

 destructibility of matter or force. 



It is not pretended that the existence of atoms has been or can be 

 proved or disproved. Some chemists think that the atomic theory is 

 the life of chemistry; others have abandoned it. Its importance is lost 

 in that of the molecular theory. And what has this accomplished to 

 justify its existence ? If we define the molecule of any substance as the 

 smallest mass of that substance which retains all its chemical proper- 

 ties, we can start with the extensive generalization of Avogadro and 

 Ampere, that an equal volume of every kind of matter in the state of 

 vapor, and under the same pressure and temperature, contains an equal 

 number of such molecules. The conception of matter as consisting of 

 parts, which are perpetually flying over their microscopic orbits, and 

 producing by their fortuitous concourse all the observed qualities of 

 bodies, is as old as Lucretius. He saw the magnified symbol of his 

 hypothesis in the motes which chase one another in the sunbeam. 

 One of the Bernouillis thought that the pressure of gases might be 

 caused by the incessant impact of these little masses on the vessel 

 which held them. The discovery that heat was a motion and not a 

 substance, foreshadowed by Bacon, made probable by Rumford and 

 Davy, and rigidly proved by Mayer and Joule when they obtained its 

 exact mechanical equivalent, opened the way to the dynamical theory 

 of gases. Joule calculated the velocity of this promiscuous artillery, 

 rendered harmless by the minuteness of the missiles, and found that 

 the boasted guns of modern warfare could not compete with it. Clau- 

 sius consummated the kinetic theory of gases by his powerful mathe- 

 matics, and derived from it the experimental laws of Mariotte, Gay- 

 Lussac, and Charles. By the assumption of data, more or less plausi- 

 ble, several mathematicians have succeeded in computing the sizes 

 and the masses of the molecules and some of the elements of their mo- 

 tion. It should not be forgotten that mathematical analysis is only a 

 rigid system of logic by which wrong premises conduct the more 

 surely to an incorrect conclusion. To claim, for all the conclusions 

 which have been published in relation to the molecules, the certainty 

 which fairly belongs to some of them, would prejudice the whole cause. 



