[ 536 ] 
mirk, that the machine might be in full play when 
the courfe was begun : The lpindle was flopped at the 
beginning and end ; the numbers read off, and were 
as follows : 
i 
The lpace between the marks was, by eftimation, 
about half a mile. 
Revert ‘ 
i ll rowing up the river, in 1 1 min. the plate made 61 y 
2d down 14. . . . 6^y 
3d up 18 and an half . 61 z 
4th down 9 and an half . 603 
yth up 1 8 620 
6 th down 10 * . . 600 
It is obfervable, that the greatefl difference, among 
the above obfervations, is between the 2d and 6th, 
being 645 and 600 ; the difference being about one 
fourth part of the whole ; the times being 14 mi- 
nutes and 10, both in going down the river : Whereas 
thofe obfervations, which differ mofl in point of time 
viz. the 3d and 4th, being performed in 18 minutes 
and an half, and 9 minutes and an half, refpedively ; 
have their revolutions more nearly alike, being 61 2 and 
603 ; which differ only by one fixty-eighth of the 
whole. From thefe obfervations I was led to think, 
that the different velocities, wherewith a veffel moves 
forwards, would make no material difference in the 
number of rotations of the plate j or, at leafl, that 
thofe differences would be lefs than the irregula- 
rities ariling from other caufes, even in trials nearly 
iimilar. 
The 
