A CENTURYS PROGRESS OF THE STEAM K.\(iL\K.' 



By Dr. K. H. Thurston. 



Twenty years ago, reviewino- the i)r()oivss of t\w st(>iiiii cnoi,,,. to 

 date, and seeking the reasons of the steady gain ol)servahle^iii the 

 eeonomy of its operation, the writer, in Ids Ilistoi-y of the (irowth of 

 the Steam Engine, remarked: 



The direction of improvement has been marked bv a continual 

 increase of steam pressure, greater expansion, pi-ovision'for obtaining 

 dry steam, higher piston speed, careful protection against loss l)y 

 radiation and conduction, and in marine engines by surface condeii- 

 sation. 



This statement and the extended discussion of the details of incthod 

 and manner of steady improvement during the time since Watt, which 

 were then and there given, apply as well to-day. and require absolutely 

 no qualitication, and the summary holds good for the ccntui-y. The 

 salient points of this progress are three: (1) lncreas(>d steam i)ressun': 

 (2) proportional increase of the "total" ratio of expansion: (H) con- 

 tinual rise in speeds of piston and of rotation. 



Of these methods, the first and second, which are in fact propciiy 

 means of attaining a single ot)ject. the widening of the tcnipci-atuiv 

 range of the engine cycle, give increased thermodynamic efficiency, 

 and the third produces lessened Avastes of heat and work by ])ermitting 

 a larger amount of work to be done by a smaller machine. Roughly 

 estimated, the gain by those methods is proportional to the increase of 

 the square root of the total range of temperatui-e worked through, 

 and to that of the reciprocal of the time occupied by a stroke of piston 

 or by a revolution of the engine, i. e.. to the increase of engine speed. 

 It will be interesting and useful to note what have been the magnitu(l«'s 

 of these quantities since, at the beginning of the century, the steam 

 engine assumed its modern form and commenced its great W(.ik of 

 producing our modern civilization. The following statements and the 

 accompanying diagrams show, approximately, perhjips with consider- 

 able and sufficient accuracy, what have been the engine speeds, the 

 expansion ratios, and the steam pressures since the now expiring cent nry 

 was born; what have been the rates of advance, and what the amount 

 of the gains effected. 



1 Reprinted from Cassier'sMa>ra/ine, Vol. XVII, IS'..1»-1!HH), ,.,.. M'l -l!«'- 



oai 



