246 M. Arago's Biographical Memoir of James fTatt. 



der at each stroke, would be about 600 cwt. This enormous 

 power, fi-equently repeated, may be obtained by means of a 

 very simple apparatus, provided we could discover a method, 

 at once prompt and economical, whereby we might produce 

 and destroy at pleasure an atmospheric pressure in a metallic 

 cylinder. 



This problem Papin resolved. His beautiful and grand 

 solution consists in the substitution of an atmosphere of steam 

 for the common atmosphere, — in the replacement of this latter 

 by a vapour which, at the boiling point, has precisely the same 

 elastic force, but with this unportant advantage, of which the 

 common atmosphere is destitute, viz., that the power of aque- 

 ous vapom- is enfeebled very rapidly when the temperature is 

 lowered, and that it alnaost wholly disappears, if the refrige- 

 ration be carried sufficiently far. I shall, therefore, adequately 

 characterize the discovery of Papin, and in a few words, by 

 saying, that he proposed to make a vacuum in large spaces by 

 means of steam, and that his method is at once prompt and 

 economical.* 



The machine in which our illustrious countryman was thus 

 the first to combine the elastic force of steam with the pro- 

 perty which steam possesses of being annihilated by cold, he 

 never executed on a large scale. His experiments were al- 

 ways made on mere models. The water which was intended 

 to produce the steam did not even occupy a distuict vessel : 

 enclosed in the cylinder, it reposed upon the metallic plate 

 which closed it beneath. This plate Papin heated directly, to 

 transform the water into steam ; and it was from the same 

 plate he removed the fire when he wished to effect the ^con- 

 densation. Such a process, barely tolerable when experi- 

 ment is intended to verify the accuracy of a principle, would 



* An English engineer, deceived, no doubt, by an incorrect translation, 

 asserted, not long ago, that the idea of employing steam in one and the same 

 machine, as an elastic force, and as a rapid means of producing a vacuum, 

 belonged to Hero. I have, however, proved, beyond dispute, that the me- 

 chanist of Alexandria never dreamed of steam ; and that in his apparatus 

 the alternate movement could have resulted only from the dilation and con- 

 densation of air proceeding from the intermittent action of tho solar rays. 



