G, W. Hough on an Automatic printing Barometer. 47 
clock-work, and allows the wheel a to make a complete revolu- 
tion. By this means the wheel W is advanced one tooth, which 
raises the screw S the z;'s5 of an inch, and consequently carries 
the point p that distance away from the disk d. 
As long as the mercury rises, the magnet m-will be operated, 
and the platinum point p will be kept the z;'55 of an inch above 
the disk d. 
If, on the contrary, the mercury falls in the siphon, the under 
side of the platinum disk d will be brought in contact with the 
point of the wire p’, thereby closing the circuit through the 
magnet m’; the armature of which allows the one tooth wheel a’ 
to make a complete revolution, thereby causing the screw S to 
be depressed the ;,',, of an inch, carrying of course, the platin- 
um point p’ with it. 
It will now be readily seen how the platinum disk d, carried 
by the float b, may always be maintained midway between the 
two points p and p’, and distant.a little less than the 3,455 of an 
inch from each. 
he barometer is of the siphon form; the inside diameter 
of the portions near the surface of the mercury is nearly one 
inch, The upper and lower portions were made from the same 
glass tube, the two being connected by a tube of smaller diame- 
ter. The experiments and observations, so far, indicate that 
there is no appreciable difference in the size of the two legs of 
the siphon. j 
The float } is of ivory ; the form a paraboloid of revolution. 
The under side of this float is very slightly concave. The diam- 
eter is one-tenth of an inch less than the inside diameter of the 
preventing 
‘ee to prevent any frictio 
wire p is attached to a fine screw, for adjusting she dis- 
These wires p and p/ are, of course, insulated by being at- 
tached to an oe 3 black as shown in the figure. The wires 
ara there points are led to the top of the screw 8, where they 
are fastened to an ivory block, after which they are conn : 
hin sien a eee lin the side of the barometertube, == 
