22 



THE POPULAR SCIENCE MONTHLY. 



Savery never fitted his boilers with the safety-valve, although it 

 was subsequently used on Savery engines by Desaguliers ; and in deep 

 mines he was compelled to make use of higher pressures than his 

 rudely-constructed boilers could safely bear. 



The introduction of his machines was, therefore, greatly retarded 

 by the fear, among miners, of the explosion of his boilers ; in fact, 

 such explosion did occur on more than one occasion. 



20. The Savery engine was improved, about 1*716 or 1718, by Dr. 

 Desaguliers, who attached to it Papin's safety-valve, and substituted 

 a jet injection from the stand-pipe into the " forcing-vessels " for the 

 surface condensation of Savery's original arrangement. 



21. The Savery engine, however, after all improvement in design 

 and construction, though a working and a useful machine, was still a 

 very wasteful one. The steam from the boiler, passing into the cold, 

 wet water-reservoir or forcing-vessel, was condensed in large quan- 

 tity, and also to a very serious extent, by coming into actual contact 

 with the water itself. 



Papin, who has already been referred to, in 1707 proposed 1 to 

 avoid this loss, to some extent at least, by the use of his piston, which 



Fig. 9. Papin's Steam-Engine, a. d. 1707. 



he interposed between the steam and the water, as in Fig. 9, which 

 is copied from a sketch given by Papin himself. 



This engine is, in principle, a Marquis of Worcester engine, in 

 which the piston E is introduced to separate the steam from the water 

 which it impels, and thus to reduce the amount of loss by condensa- 

 tion. 



This engine was never constructed, except experimentally, how- 

 ever, and is principally of interest in a history of the steam-engine 

 from the fact that it was a useful suggestion to succeeding inventors. 



Papin had, as early as 1698, abandoned his earlier but more ad- 



1 " Nouvclle Maniere de lever l'Eau par la Force de Feu, mise en Lumiere." Par 

 M. D. Papin, Docteur en Medecine, Professeur en Mathematique a Cassel, 1707. 



