JAMES WATT. 35 



exposed to the fire. He also ascertained the quantity of coals 

 necessary for the evaporation of any given quantity of water, 

 the heat at which water boils under various pressures, and many 

 other particulars of a similar kind which had never before been 

 accurately determined. 



Thus prepared by a complete knowledge of the properties ot 

 the agent with which he had to work, he next proceeded to 

 take into consideration, with a view to their amendment, what 

 he deemed the two grand defects of Newcomen's engine. The 

 first of these was the necessity arising from the method employed 

 to concentrate the steam, of cooling the cylinder, before every 

 stroke of the piston, by the water injected into it. On this 

 account, a much more powerful application of heat than would 

 otherwise have been requisite was demanded for the purpose of 

 again heating that vessel when it was to be refilled with steam. 

 In fact. Watt ascertained that there was thus occasioned, in the 

 feeding of the machine, a waste of not less than three-fourths 

 of the whole fuel employed. If the cylinder, instead of being 

 thus cooled for every stroke of the piston, could be kept per- 

 manently hot, a fourth part of the heat which had been hitherto 

 applied would be found to be sufficient to produce steam enough 

 to fill it. How, then, was this desideratum to be attained? 

 De Caus had proposed to effect the condensation of the steam 

 by actually removing the furnace from under the boiler before 

 every stroke of the piston; but this, in a working engine, 

 evidently would have been found quite impracticable. Savery, 

 the first v/ho really constructed a working engine, and whose 

 arrangements, as we have already remarked, all showed a very 

 superior ingenuity, employed the method of throwing cold 

 water over the outside of the vessel containing his steam — a 

 perfectly manageable process, but at the same time a very 



