Rotatory Steam-Engine. 47 



a pecuniary saving of coals, whicli, in the constant use of a 

 machine, is of much more importance than its first cost. That 

 this saving is really effected in the present machine, will be suf- 

 ficiently evident to those who possess mechanical knowledge ; 

 and for the conviction of those who do not, I have subjoined 

 the diagram by which the action of the ordinary crank may be 

 demonstrated. If the crank rod be so placed as to act either 

 from above or below, it will have no power at all (figs. 1 and 8.) 

 to turn the crank round, while it is, in either of the two situations 



Fig. 2, 



Fig. 3. 



where the crank and rod are in one line, as at A and B, but 

 it will have the greatest possible power upon it at those instants 

 when it is at two other intermediate points (M and N, figs. 

 2 and 4), the consequence of which is, that while the power 

 forces the crank to revolve, it increases in the first quarter re- 

 volution from zero to a maximum, and diminishes in the second 

 quarter from the maximum to zero, and so on for each half revo- 

 lution. The loss of power attendant on the use of the crank, is 

 found in figures to be nearly one-third of the whole."" 



Mr Aldersey expresses clearly the sentiments of a host of in- 

 ventors, all of them pursuing the main object of doing away 

 the imaginary loss of power occasioned by the crank. I am 

 sorry to add, that some eminent standard writers on the steam- 

 engine have advanced the same doctrines. 



