432 
NATURE 
[Sepz. 28, 1871 

rest during a period of fifteen minutes, the time required 
for elevating the hammers H and H’. As soon as this is 
accomplished, the lever begins to rise slowly by means of 
the double snail on the hour shaft, the time required for 
traversing the drum being about fifteen minutes. When 
the position of the lever is such that the carriage in the 
rear of the clock touches the float in the shorter leg of the 
siphon, an electric current is established through the 
magnet, F, which unlocks the hammer H, causing the pen 
G to make a record on the drum sheet. After the lever 
has reached the top of the drum, it remains at rest fifteen 
minutes while the hammers are being raised, when it is 
gradually depressed. So soon as the platinum wires— 
attached to the carriage over the thermometers—touch the | 










































with the mercury in the barometer. This screw carries a 
pencil, which traces upon a revolving cylinder or roll of 
paper a line showing the minutest movements of the 
column of mercury for every minute in twenty-four hours. 
This same screw also gives motion toa series of wheels | 
which carry types, by which, at the end of every hour, 
the height of the column of mercury is printed on a slip 
of Dapey to the accuracy of the thowsandth part of an 
inch : 
One of the most beautiful and simple contrivances used 
is a Wild’s Self-registering Barometer, of which we givea 
cut one quarter the actual size. It scarcely needs expla- 
nation, except to say that the tube A is suspended in a 



surface of the mercury in the thermometer tubes, electric 
currents are established through the magnets F and J, 
simultaneously or successively unlocking the hammers, 
and, as the case may be, making records as before. 
A complete double motion of the lever requires one 
hour. During this time the barometer and wet and dry 
bulb thermometers have each been recorded once. The 
records of the barometer and thermometers differ in time 
about half anhour. The wet and dry bulb thermometers 
are recorded within about one minute of each other, de- 
pending on the difference between them. 
One of the most marked and wonderful features of the 
invention of Prof. Hough is that it prints its own records. 
And this is done by a single screw, which rises or falls 

FIG. 9. —WILD’S SELF-REGISTERING BAROMETER (BAROMETER TUBE MOVEABLE) 
cistern of mercury, represented on the left of Fig.9. As 
the atmospheric pressure changes, the level of the mercury 
changes in the cistern, and the tube A rises or falls as the 
atmospheric pressure increases or diminishes. The weight 
of this tube as it floats in the mercury, and also that of 
the arm /, which supports it at G, is exactly balanced by 
the arm //, to which is attached a sliding weight, ///, 
adjustable by a small thumb-screw. 4’ is a steel crayon- 
holder fixed to the balance 7 77, and to which is fixed a 
crayon, c, whose point in seen in B to impinge upon a 
sheet of paper, 7 7, This sheet s moved by clock-work. 
When the atmospheric pressure is increased, the tube 4 
is forced to rise a little out of the mercury in which it 
