PRESIDENTIAL ADDRESSES. 539 



they so ordered ? Nevertheless, I believe all, or 

 nearly all, his scientific contemporaries agreed with 

 Daniel Bernoulli in answering this question 

 affirmatively. Very soon after the middle of the 

 eighteenth century Father Boscovich 1 gave his 

 brilliant doctrine (if infinitely improbable theory) 

 that elastic rigidity of solids, the elasticity of 

 compressible liquids and gases, the attractions of 

 chemical affinity and cohesion, the forces of 

 electricity and magnetism in short, all the 

 properties of matter except heat, which he attri- 

 buted to a sulphureous fermenting essence are to 

 be explained by mutual attractions and repulsions, 

 varying solely with distances, between mathe- 

 matical points endowed also, each of them, with 

 inertia. Before the end of the eighteenth century 

 the idea of action-at-a-distance through absolute 

 vacuum had become so firmly established, and 

 Boscovich's theory so unqualifiedly accepted as a 

 reality, that the idea of gravitational force or 



1 Theoria Philosophic Nattiralis Redacta ad unicam legem 

 virium in natura existentium auctore P. Rogerio Josepho Bosco- 

 vich, Societatis /esu, 1st edition, Vienna, 1758; 2nd edition, 

 amended and extended by the author, Venice, 1 763. 



