39® Dr. Herschel's Description of a 
from the centre of the square hole, I have mentioned, in the 
dial-plate, for shewing the degrees ; and a small square por- 
tion, a little more of one than the other of the two wheels, 
may therefore be seen, in front of the dial-plate, through the 
opening in it. 
These wheels carry contrate teeth on the inside, and a small 
dial-plate on the back. The face of the dial-plate of the wheel 
which presents itself at the right, carries the units of the de- 
grees ; 1, 2, 3, 4, 5, 6, 7, 8, 9, o ; while that on the left has a 
blank which remains till the o of the first appears. Upon the 
axle of the barrel, close to the frame-plate on the outside, is 
fixed a long counterpoised contrate pallet ; which at every 
revolution sweeps over one of the teeth of the first wheel, of 
which there are ten. The shape of the pallet must be like the 
barb of an arrow ; but more obtuse, that it may take as much 
time in entering very obliquely into the teeth as possible, to , 
avoid a sudden shock. The movement will even then be found 
to be quite quick enough, for shewing almost instantly the 
proper degree of polar distance. But to counteract the sud- 
den stroke of the long pallet, there is over each wheel a small 
lever, see a b, fig. 42. that rests with its end between the two 
uppermost teeth c d ; and its shape is that of a very obtuse 
angle, such as 160 degrees. The point of the angle sinking 
down between the two teeth, by its slope both ways, prevents 
their overshooting. The lever is held down with a very weak 
spring, ef the point of which touches the lever at e, near 
the place of its pivot. This method will even throw back the 
figure upon the dial, if it should have been overshot a little. 
Care must be taken to let all this work be light, that no great 
force may be required in the long pallet to move it. 
