182 APPENDIX. 



Russell, Esq., a gentleman to whom practical science is much indebted. One of the leading 

 objects of this paper, which is printed in the Edinburgh New Philosophical Journal for 

 January 1838, is to show that no loss of power is sustained by the intervention of the crank; 

 but, in doing this, it should be remarked, that the author has throughout his paper discussed 

 only the particular case in which the moving power acts on the crank in parallel lines, or in 

 which the connecting rod is supposed to be of infinite length ; and that this necessarily 

 reduces many of his statements into mere approximations, when the subject is generally con- 

 sidered. Mr. Russell has, however, handled the subject with considerable power, and his 

 remarks are, perhaps, sufficiently precise for the object he had in view, viz., to dispel the 

 delusion under which many practical men labour with respect to the nature of the crank, that 

 it is attended with a loss of nearly one-third of the power. It is well known that persons are 

 to be found who have been the subjects of this delusion, as well as inventors who have been 

 its victims, but we cannot concur with Mr. Russell that " some eminent standard writers on 

 the steam engine have advanced the same doctrines." Most writers who are accustomed to 

 treat these matters scientifically have doubtless considered that no reasonable dispute could 

 possibly be entertained, and have thought it unnecessary to make any declaration on the 

 point in question. We may, however, be allowed to refer to one exception. At page 137 of 

 " Hann and Dodd's Mechanics for Practical Men," the very question is taken up, and com- 

 prehensively disposed of, in the following paragraph : 



" In the crank, as applied in the steam engine, the effect which is produced, is to the effect, 

 " were the force to act perpendicularly on the crank all the way round, as twice the diameter 

 " of a circle is to the circumference ; in consequence of which, many practical men have 

 " considered that there is a corresponding loss of power by using a crank ; without ever 

 " considering that the piston, or moving power, only moves through twice the diameter of the 

 " crank's orbit, while the crank moves through its whole circumference. For here the same 

 " principle holds good as in all other mechanical contrivances, viz., the power multiplied by 

 " the space which it passes over, is equal to the weight or resistance multiplied by the space 

 " which it passes over." 



These statements have since found their way into other mechanical works of more recent 

 date ; and it is certainly of some moment that practical men who have not the means of 

 following out theoretical investigations of these subjects, should be thus guarded from an error 

 by which many of them have been so widely misled. That no power is gained or lost by the 

 use of the crank has already been established on dynamical principles at the commencement 

 of this paper. We are not, however, to conclude that this principle is at all peculiar to the 

 crank. It is well known to apply to every combination of the five elementary powers, and by 

 the principle of virtual velocities it may easily be shown that it is an universal property of 

 mechanical arrangement, that with every possible mechanical combination, no power can be 

 gained or lost, if we except the resistances occasioned by friction. 



