207 niMxivs*! 



Proceedings of the Royal Society. 



In consequence of the lamented death of H. R. H. the Duke of 

 York, the business of the Royal Society was not resumed until the 

 25th of January ,when a paper was communicated by Davies Gilbert, 

 Esq., *• On the Expediency of assigning Specific Names to all 

 such Functions of Simple Elements as represent definite Physical 

 Properties ; illustrated by an Investigation of the Machine moved 

 by recoil, and also by some Observations on the Steam-Engine.** 



In this paper the author presses the necessity of distinguishing 

 by separate appellations all functions which measure the intensity 

 of physical properties, and adduces, in favour of his argument, the 

 controversy which ensued soon after the application of mathemati- 

 cal expression to the laws of motion, when it was contended, on 

 the one hand, that the weight of a moving body multiplied into its 

 velocity, was the measure of the motion ; and on the other, that the 

 weight should be multiplied into the square of the velocity, to obtain 

 such measure. At length it was ascertained that these views were 

 not really discordant, and the terms momentum and impetus, respec- 

 tively applied to them, ended the discussion. The author then 

 observes, that neither of these terms is a correct measure of the 

 efiective action of machines, the criterion of which is the force 

 exerted, multiplied by the space through which it acts. Mr. Watt 

 expresses this numerically, in reference to the steam-engine, by 

 the term duty ; and the raising of a pound weight to the height of 

 one foot has been made by him the dynamic unit. For this 

 measure, Mr. Gilbert proposes the term efficiency^ and retains 

 the term duty for a similar function, indicative of the work per- 

 formed ; and by comparing these two functions, a measure of the 

 actual work performed by any machine may be obtained. 



Mr. Gilbert then illustrates the utility of this term in investi- 

 gating the mechanical power of the recoil-engine, and shows the 

 impossibility of economically applying steam on such a principle. 



Some observations on the efliciency of steam, and on the com- 

 parative powers of different engines, concluded this communi- 

 cation. 



At this meeting. Professor Jameson s name was ordered to be 

 inserted in the printed lists of the Society, he being unable at 

 present to attend in London for personal admission. 



