IGO Steam-Engine — Physics, ^'c. 



sible in the steam, which thereupon acquires expansive force 

 to an unhmited degree : that this force increases geometri- 

 cally ; or, that every accession of about 30° of heat, nearly 

 doubles its power at those stages of progression ; that when 

 the pressure at a high temperature is taken oflf, or the steam 

 allowed to flow, there is an instantaneous and rapid production 

 of steam ; a fact which proves there can be no necessity of a 

 large space for the steam to form in above the water, provided 

 it be sufficient to prevent water from issuing with the steam, 

 and, therefore, that boilers of a small cylindrical form are best. 



It may be a fair question, why Mr. Watt did not further 

 employ this principle of expansive force ? We may readily 

 conceive of several motives to the contrary. Watt and Bolton's 

 engines were in great demand ; they gave entire satisfaction, 

 and the work they performed saved so much labour as to 

 afford the purchase at a high price. The public had gained 

 immensely by this better form of the engine, and Mr. Watt 

 enjoyed the benefits of the patent he had obtained ; and, at a 

 later period, this preference was increased by an accident which 

 happened to Trevethick's engine, though caused by gross mis- 

 management, that would have been equally fatal to any other. 



From an investigation, by a committee of parhament, into 

 the causes of the several fatal explosions of steam-engine 

 boilers within a few years, published in Tillock's Magazine, 

 vol. 1., it appears that in every instance the accident was fairly 

 attributable to neglect or mismanagement. Many competent 

 persons were summoned to give their opinions ; and through 

 the contrariety of their testimony, the prevalent opinion ap- 

 pears to have been, that cast-iron boilers cannot be safe ; that 

 as many engines of high steam as of low are now used in Eng- 

 land, but that the high are much the most economical in fuel 

 and cost ; that they are more safe, if properly constructed ; it 

 being argued by some, that boilers for steam of 100 pounds to 

 the inch, are easily made of strength to sustain 500 pounds ; 

 this excess being much greater than in those constructed for 

 low steam, makes them comparatively the safest, as the safely 

 valves are less liable to be accidentally prevented from vent- 

 ing the steam.- 



