SECT. 



THE STEAM ENGINE. 43 



discovery of a new law of the expansibility of steam. This law of expansibility he 

 stated, with much confidence, as the result of experiment ; but no doubt he had 

 deceived himself. His assumed law of expansion is, that steam generated at any 

 number of pounds above the pressure of the atmosphere will expand to an equal 

 number of times its volume, and still be equal in elastic force to the pressure of the 

 atmosphere, the temperature being unaltered : hence steam generated at forty 

 pounds on the square inch was expected to expand to forty times its bulk, and yet 

 be equal to the elastic force of the atmosphere. But it is a well-known law of the 

 expansion of fluids, that the temperature being constant, the bulk is inversely as 

 the pressure ; and calling the pressure of the atmosphere fourteen pounds, we have 

 14 : 14+40 : : 1 : 4, nearly. Therefore steam generated at fifty-four pounds on 

 the square inch, or forty pounds above the pressure of the atmosphere, would 

 expand only to four instead of forty times its volume. (See art. 120.) And though 

 Woolf s assertions were so directly opposed to the laws of the constitution of elastic 

 fluids, they have found their way as undoubted experimental truths into works 

 which ought to have high claims to respectability. 



The employment of high pressure steam to act expansively by means of a double 

 cylinder, gives the utmost degree of power in the most equable manner and with 

 the most safety : hence either for machinery engines, or mine engines, it seems 

 the most economical mode of obtaining power. I object to strong steam on account 

 of its danger,- but my readers may not have like apprehensions. Woolf's other 

 patents are for projects of little if any value. 



58. It would be an omission to pass without notice the exertions made by 

 Oliver Evans about this period to get into use the high pressure steam engine. 

 His scheme for employing it had not at first many supporters, and he had some 

 rivals. His engine differs little from that of Trevithick and Vivian in construction, 

 but from a work called ' The Abortion of the Young Steam Engineer's Guide,' 

 it appears, that the expansive force of the steam was to be employed. The ' Abor- 

 tion' is a curious work ; it betrays that strange mixture of absurd speculation and 

 indistinct perception of truth, which distinguishes the generality of enthusiastic 

 projectors, and is valuable only to those who can select by means of previous 

 knowledge or experience. A volcanic steam engine, and the idea of employing 

 the force of solar heat by means of a burning glass to work an engine, are among 

 his projects. 



59. The claims of our American brethren to improvement, and to judicious 

 construction and application, are however much stronger than those of our conti- 

 nental neighbours ; and of American claims we have reason to speak with pride 

 rather than with other feeling. British genius and industry have not been extin- 

 guished by transplanting to another climate. It is true that many of the 



