340 PHILOSOPHICAL TRANSACTIONS. [aNNO 1759. 



the cylinder e, iii the same manner as the ferrule aa slides on the cylinder b ; 

 the outer end of the socket at gg is formed into a sort of button ; by pushing 

 it, the hollow cylinder will move backwards and forwards, or turn round at plea- 

 sure on the cylindrical parts of the axis b and e. ee, ii, oo, represent the sec- 

 tion of a brass ferrule, also fixed on the hollow cylinder : the edge of this ferrule 

 ee is cut into teeth, in the manner of a contrate wheel ; and its edge oo is cut 

 in the manner of a ratchet. 



Of consequence, when the plate bddb is pushed close to the ferrule d, the 

 teeth of the ferrule ee will lay hold of g, a pin fixed into the axis ; by which 

 means the hollow cylinder is made to turn along with the wheel and axis : but 

 being drawn back by the button gg, the hollow cylinder is disengaged from the 

 pin G, and ceases turning. Note. The weight in the scale is prevented from 

 running back, by a catch that plays in and lays hold of the ratchet oo. By this 

 means the hollow cylinder on which the cord winds, and raises the weight, is put 

 in action and discharged from it instantaneously, while the wheel is in motion : 

 for without some contrivance of this kind, it would not be easy to make this 

 sort of experiments with any tolerable degree of exactness. 



The use of the apparatus now described will be rendered more intelligible, by 

 giving a general idea of what I had in view ; but as I shall be obliged, says Mr. 

 S., to make use of a term which has heretofore been the cause of disputation, I 

 think it necessary to assign the sense in which I would be understood to use it ; 

 and in which I apprehend it is used by practical mechanics. The word Power * 

 as used in practical mechanics, I apprehend to signify the exertion of strength, 

 gravitation, impulse, or pressure, so as to produce motion: and by means of 

 strength, gravitation, impulse, or pressure, compounded with motion, to be 

 capable of producing an effect : and that no effect is properly mechanical, but 

 what requires such a kind of power to produce it. The raising of a weight, 

 relative to the height to which it can be raised in a given time, is the most 

 proper measure of power ; or, in other words, if the weight raised is multi- 

 plied by the height to which it can be raised in a given time, the product is the 

 measure of the power raising it ; * and consequently, all those powers are equal, 

 whose products, made by such multiplication, are equal : for if a power can raise 

 twice the weight to the same height ; or the same weight to twice the height, 

 in the same time that another power can, the first power is double the second:* 



* All these preliminary remarks about power, evince a considerable degree of confusion in Mr. 

 S.'s mind on mechanical power or force, and the measure of the same. With some good practi- 

 cal notions on machinery, he contrived to make some useful experiments ; but unfortunately, for 

 want of some more precise ideas on the theory of physics, he has vitiated many of the conclusions, 

 often making them appear to be very different from those determined by theory, while, rightly de- 

 duced, they are found nearly to agree. 



