16 THE HISTORY OF [SECT. i. 



ledge, each furnished a man of science to participate in the glory of the important 

 discovery : that Papin in Germany, Savery in England, and Amontons in France, 

 were each occupied in studying the means of making use of the action of jire for 

 moving machines ; but the first suggestion of the idea, in an intelligible form, he 

 acknowledges to be due to the Marquis of Worcester. Belidor closes his historical 

 notice, by remarking, that all the fire engines that had been constructed out of 

 Great Britain, had been executed by English workmen ; and then proceeds to 

 describe the atmospheric engine at Fresnes, near Conde, in that minute, clear, and 

 practical manner, which renders his writings so valuable. To the theory of the 

 action of steam Belidor added nothing ; and the formulae he has given for calcu- 

 lating the load to be lifted by an engine are neither very simple nor accurate : like 

 those of Beighton, they apply only to the statical equilibrium of the machine. 



1741. JOHN PAYNE. 



16. The first direct experiment to determine the density of steam was made 

 by John Payne. * His process was well devised, but wanted the addition of a 

 thermometer. He took a copper globe twelve inches in diameter, having two 

 cocks fitted to it, and a small valve. The vessel thus prepared was hung over a 

 large vessel, in which water was rarefied into steam, and by a pipe the steam was 

 admitted at one of the cocks into the globe, and the other being also open, the 

 steam being allowed to blow through, forced out the air that was in the globe, and 

 supplied its place ; when both cocks were suddenly shut, and the globe taken down 

 and hung over a vessel of cold water with the lower cock immersed in water. The 

 cock was opened under water, on which the water rushed violently into the globe 

 till it had supplied the vacuum, when the cock was again shut, and the globe, 

 with the water, was put in the scales, and found to weigh 713 oz., which taken 

 from 727 oz. the whole weight before, there remains only 14 oz. for the dif- 

 ference ; from which he inferred that all the air was nearly excluded out of the 

 globe by the steam. He again excluded the air out of the globe with steam as 

 before, and both the cocks being closed, with the globe full of steam, he put the 

 globe in the scales, and it weighed 202-5 oz. He then opened one of the cocks 

 and let in the air, and by adding weight in the other scale it was found to weigh 

 203 oz., which showed that the weight of the air the globe contained was '5 oz. 

 or 218'75 grains. The globe being filled with steam as before, and condensed 

 with cold water on the outside of the globe, and the metal again made very dry, 

 and the air let into the globe, the water from the condensed steam was found to 

 weigh 96 grains. It is worthy of remark here, that this gives the density 



1 PhiL Trans, vol. xli. p. 821. or Ab. vol. viii. p. 518. 



