32 THE HISTORY OF [SECT. i. 



37. The theory of the steam engine still made small progress, though it 

 excited some degree of attention. 



Bossut had described an atmospheric engine in the first edition of his ' Hydro- 

 dynamique,' in 1771, with some formula for its statical equilibrium; in the 

 edition of 1786, he investigated the proportion of counterweight, but for a particular 

 case, and not including the actual circumstances of the moving forces. 



38. A rotary engine was proposed in 1789 by Cooke, * and a patent was 

 obtained for one in 1790 by Bramah and Dickinson, 2 and for another in 1791 by 

 Sadler. 3 The peculiar construction of all these engines I need not describe, as the 

 principle of a rotary engine will be shown to be attended by a loss of effect, which 

 mechanical combinations cannot remove. (See Sect, iv.) 



39. Bramah and Dickinson's patent included three varieties ; the most simple 

 of which is designed with pistons sliding in an eccentric wheel, the steam to enter 

 at s ; and the opening to the condenser being at c, the pressure causes the smaller 

 wheel to revolve, and the pistons to slide in it. All the varieties are specimens of 



Fio. 8. 



that beautiful style of executing machinery, which Bramah contributed so much 

 to introduce in this country, and which has been carried to such high perfection 

 by his pupil, the celebrated Maudslay. 



1790. BETTANCOURT. 



40. Chev. Bettancourt, who was employed by the Spanish government to 

 collect models of hydraulic machines, made a series of experiments on the force of 

 yapour of water and of alcohol, at different temperatures. They are more accurate 

 than those which were at that time before the public, but still had not that pre- 

 cision which is necessary to develop the laws of the force of vapour. He made a 



1 Repertory of Arts, vol. iii. p. 401. 1795. * Idem, vol. ii. p. 73. 



3 Idem, vol. vii. p. 170. 



