G. W. Hough on an Automatic printing Barometer. 51 
A sectional view of the combination is shown in fig. 4, where 
Xand Y are two vertical stee 
axles. The final result ex- 
pressed in thousandths of an 
inch, is found on the axle x, 
where w is the units wheel, » 
t tens, and A the hundreds; 
or where the thousandth of 
an inch is the unit of meas- = 
ure, uw will represent thou- 4 mg ATTILATER 
sandths, ¢ ugndeaiehe od ee 
h tenths of an inch. pM sa ts ca Om Bik 
The wheel u, may be sup- Mz==> 
posed to have ten teeth, and 
(50) pil 
one tooth at each impulse, each tooth will represent the 73455 0 
complete revolution, it will have advanced @ one tooth or one- 
tenth of a revolution; consequently the wheel a will always ex- 
press the hundredths. : 
d 
But let us go a step further, and see how we get our tenths. 
The wheels a, 2, we have shown, indicate the hundredths; we 
