{ aso J 
XXV. A Memoir on the lest Method of measuring 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, 
F.L.S., of the Royal Militery Academy, Woolwich. 
[Continued from p. 68.] 
Article V. 
Description of the escapement of the new watch, which pre- 
serves isochronism in the regulator, and freedom in its 
vibrations. 
At that precedes has proved to us, that the best, the most 
certain, and even the only method of bringing a marine 
clock to the requisite degree of truth, is, as has been said, 
to render the vibrations of its regulator as free and as iso- 
chronous as possible * ; this is what I have followed. It 
thas been seen in what manner I have arrived at it,—by the 
suspension of the regulatur. But to preserve to it this free- 
dom, so precious in its application to the wheel-work, it is 
necessary to employ an escapement totally different from 
those which have hitherto been made. 
Of what use would it have been, in effect, to have anni- 
hilated friction in the suspension, if by the nature of the 
escapement the regulator had met with twenty times as 
much? This is what would have happened if I had had re- 
course to the cylinder, or to other dead escapements, which, 
qn the end, amount to the same as this first; the friction 
being always very much increased. I dare affirm that it 
was, in a great measure, on account of the escapement that 
most of the attempts to discover the longitude by clock-work 
have miscarried. We may consult on. this subject the re- 
marks made by M. Sully on marine clocks. 
The following is an experiment which will show how 
considerable the friction is even in the best escapements. 
T took a cylinder watch, by Mr. Graham, and turned the 
* I cannot here agree in opinion with Mr. Daniel Bernoulli, who recom- 
mends (i/idem pag. 43) to augment purposely the resistance of the air to the 
motion of the balance, and to add to it three or four small wings. 
Vol. 26. No. 102. Nov. 1806. I ferrule 
