G. W. Hough on an Automatic printing Barometer. 45 
elements is effected. 
Attention was then given to determining the degree of delicacy 
with which changes of the mercury surface could be represented 
by this process. It was found by experiment that a motion of 
less than -0005 of an inch was readily shown, a quantity within 
the limits of reading of a first class standard barometer 
_ The next step was to devise the proper mechanism for repeat- 
Ing the motion thus transferred, and recording it in some legible 
rm. <A finely cut screw was considered as best adapted to 
measure such minute intervals of space. To this screw a for- 
ward or reverse motion was given by a double system of clock 
work, each operated by an electro-magnet in connection with 
the float, and raising or lowering the screw by intervals corres- 
ponding with the changes indicated in the mercury column. 
n respect to the permanent record of results, it was decided 
not only to attempt the production of a linear diagram or curve 
of atmospheric pressure, as an interesting method of alg. 
the recorded changes to the eye, but to avoid the tedium an 
uncertainty of measuring + such results, by producing at the 
We at once decided to adopt the “ make” circuit; for so long as 
is no motion, there will be no consumption of battery 
: | which we have adopted for rding 
transits is essentially that of Daniell ; peipbaines copes being 
exciting agent. A battery of this kin main sufi- 
