[ 193 J}. 
XXXIII. A Memoir on the best Method of measiiring Time 
at Sea, which obtained the double Prize adjudged by the 
Royal Academy of Sciences; containing the Description 
of the Longitude Watch presented to His Majesty the 5th 
of August 1766. By M. Le Roy; Clock-maker to the 
King. Translated from the French by Mr. T. S. Evans, 
P.L.S., of the Royal Military Academy, Woolwich. 
{Concluded from p. 146.] 
Par? IV. 
Further observations on the construction of the new watch, 
by which we confirm the advantages of the methods which 
are used: difficulties in some of these methods removed : 
recapitulation, &c. 
I PROPOSE, in this fourth part, to clear up sore articles 
that I could not give with sufficient extent in the pre- 
ceding without removing one object from another, which 
when brought together mutually render each other more in- 
telligible. 
One of those whith most requires to be explained is the 
motive force. 
This part of my watch, perhaps, may to some persons 
appear neglected: it has no fusee; nor have I used the me- 
thods which Messrs. Leibnitz*, Hook f, Huygensf, Sully §, 
Harrison ||, and others, have applied to render the magnitude 
of the vibrations, and the force which maintains them, con- 
stant. According to this method, the watch has, we know; 
two motive forces; of which one that only moves the last, 
or the two last wheels, is wound up by the other, which 
being successively stopped, or put at liberty by means of any 
detent, becomes foreign to the regulator. 
I answer, that by supposing these methods to possess 
any advantage, nothing would prevent their application to 
nmiy chronometer; they ate known to men of science and 
* Journal des Savans 1675. + Ibid. 
+ Horologia oscillatoria. § Descrip. d'une Pendule Marine. 
|| Gazette du Commerce. 
Vol. 26, No. 103. Dec. 1806, N artists, 
