G. W. Hough on an Automatic printing Barometer. 49 
In order that the wheels a and a’ may not revolve with too 
great rapidity, a train of clock work is connected, consisting 
of two additional axles, a fan being attached to the latter, by 
* means of which the motion can be regulated to any desirable 
velocity. Three axles would undoubtedly be sufficient, the 
barrel axle, the axles a, a’, and an additional one for the fan. 
We adopted the present form, because we happened to have 
a couple of clock movements at hand, and used them just as. 
they were. 
In order to prevent the cogs of the wheels a, a’, from com- 
ing to the circumference of W at the same time, during rapid 
oscillations of the barometrical column, two circuit-“ breakers” 
were connected; so that, at every revolution the circuit is 
interrupted, and neither wheel can revolve until they both are 
at rest, 
Fig. 8 is a perspective view of the apparatus as it is when in 
operation. The frame work for supporting the barometer tube 
and other mechanism is of black walnut two inches thick, which 
is firmly fastened to the east wall of the west transit room. 
wall is built of brick, and is two feet thick, so that the whole 
apparatus occupies a ve osition. : : 
laving given a general idea of the mechanism for causing the 
Screw S to follow the motions of the barometrical column, we 
will show how the curve of pressure is recorded, as well as the 
printed results, 
ter, having 80 teeth; this wheel is geared into one of 40 teeth 
Carrying an 80-tooth wheel on the same axle. This second 
80-tooth wheel is geared into a 50-tooth wheel, which operates 
the screw S', fig. 8, of 26 threads to the inch. To this screw is 
attached an arm, carrying a pencil which traces the curve of 
Pressure on the revolving cylinder 0. : ; 
From this arrangement, the curve is magnified a little more 
than three times the barometrical pressure. It would have been 
an easy matter to adapt the second screw and cog wheel, so oa 
7 
