D'ALEMBERT. 411 



namely, that it is a body composed of very minute par- 

 ticles, separate from each other, and capable of free 

 motion in all directions. He applies the general dyna- 

 mical principle to the consideration of resistance in all its 

 views and relations, and he applies the calculus to the 

 solution of the various problems with infinite skill. It is 

 in this work that he makes the most use of that refine- 

 ment in the integral calculus of which we shall presently 

 have occasion to speak more at large, as having first been 

 applied by D'Alembert to physical investigation, if it was 

 not his own invention. But the interval between 1744 

 and 1752 was not passed without other important con- 

 tributions to physical and analytical science. In 1746, 

 he gave his Memoir on the general theory of Winds, which 

 was crowned by the Royal Academy of Berlin. The 

 foundation of this able and interesting inquiry is the 

 influence of the sun and moon upon the atmosphere, the 

 aerial tides, as it were, which the gravitation towards 

 these bodies produces ; for he dismisses all other causes of 

 aerial currents as too little depending upon any definite 

 operation, or too much depending upon various circum- 

 stances that furnish no precise data, to be capable of 

 analytical investigation. The Memoir consists of three 

 parts. In the first he calculates the oscillations caused 

 by the two heavenly bodies supposing them at rest, or the 

 earth at rest in respect of them. In the second, he 

 investigates their operation on the supposition of their 

 motion. In the third, he endeavours to trace the effects 

 produced upon the oscillations by terrestrial objects. The 

 paper is closed with remarks upon the effects of tempera- 

 ture. The whole inquiry is conducted with reference to 

 the general dynamical principle which he had so hap- 



