THE GROWTH OF THE STEAM-ENGINE. 



J 35 



facture of musical instruments, making himself familiar with the sci- 

 ences, and devising improvements in the construction of organs. 



His reading was still very desultory; but the introduction of the 

 Newcomen engine in the neighborhood of Glasgow, and the presence 

 of a model in the college collections, which model was placed in his 

 hands in 1763 for repairs, led him to study the history of the steam- 

 engine, and to conduct for himself an experimental research into the 

 properties of steam, using a set of improvised apparatus. 



31. The Newcomen model, as it happened, had a boiler, which, 

 although made to a scale from engines in actual use, was quite in- 

 capable of furnishing steam enough to work the engine. 



It was about nine inches in diameter, and the steam-cylinder was 

 two inches in diameter, and of six inches stroke of piston, arranged as 

 in Fig. 13. 



This is a picture of the most 

 carefully-preserved treasure in the 

 collections of the University of 

 Glasgow. Watt at once noticed 

 the defect referred to, and imme- 

 diately sought first the cause and 

 then the remedy. 



32. He soon concluded that the 

 sources of loss of heat in the New- 

 comen engine which loss would 

 be greatly exaggerated in a small 

 model were : first, the dissipation 

 of heat by the cylinder itself, which 

 was of brass, and was both a good 

 conductor and a good radiator ; 

 secondly, the loss of heat conse- 

 quent upon the necessity of cool- 

 ing down the cylinder at every 

 stroke in producing the vacuum ; 

 and, finally, a loss of power was 

 due to the existence of vapor be- 

 neath the piston, the presence of which vapor was a consequence of 

 the imperfect method of condensation which characterizes the New- 

 comen engine. 



He first made a cylinder of non-conducting material wood soaked 

 in oil and then baked and found a decided advantage in the econ- 

 omy of steam thus secured. 



He then conducted a series of experiments upon the temperature 

 and pressure of steam at such points in the scale as he could readily 

 reach, and, constructing a curve with his results, the abscissas repre- 

 senting temperatures, and the pressures being represented by the 

 ordinates, he ran the curve backward until he had obtained approxi- 



Fig. 13. The Newcomen Model. 



