48  G.W. Hough on an Automatic printing Barometer. 
and passes down in the mercury on the side of the float 3. This 
wire is also connected with one pole of the batter 
The principle employed for giving motion to the screw 5, 
which follows the fluctuations of the mercurial column, has been 
taken from the stop work long used on clocks. The barrel of a 
clock on which the cord is wound usually has a one-tooth wheel 
on its axis; and at every revolution re the barrel, a cog wheel 
made to advance one tooth. cog w wheel i is, of course, 
sitesi detuned from the barrel tooth wheel, except when in 
the act of advancing the tooth. In fig. 2, we have a vertical — 
view of a portion of the mechanism, showing the method of 
communicating motion to the screw S. The one tooth wheels, 
a a’, when at rest occupy the positions as shown in the drawing; 
and being detached from the cog wheel W, it is free to move in 
either direction. The screw S, which is shown in fig. 1, is raised 
2. 
or de by the sakes of the wheel W. one 
wheels @ and a', moving in the direction of the arrows, give 
opposite motions to the Ww ea W ; the office of a being toelevate 
“The po vy for exec motion to the wheels a and a’ is 
ordinary clock work, each being directly acted on by the barrel — 
wheel, which is driven by a weight. One revolution of the bar 
rel co corresponds to twelve of pth wheels a anda’, The to 
which are attached a, a’, carry another wheel having a single 
half-tooth, as shown in the drawing, fig. 2, which, — — 
magnet, hol 
-@ little projection on the armature of the 
wheel in the position as shown in the figure, 
