278 
THE FLORIST AND POMOLOGIST. 
[ Decembeu, 
The thermometer tube is nicely poised on pivots between two upright pieces 
of brass, these upright supports being securely fastened to an alabaster stand, on 
each side of which is fixed a small brass pillar, having another piece of metal, 
either of platinum or aluminum, screwed on to its top, while beneath the tube 
another point of the same metal is fastened at each end opposite the pillar, so that 
on whatever side the tube may descend, it will bring in contact these two points, 
namely, that on the pillar and that on the thermometer. To the two brass 
j^illars, which are insulated, the conducting wires (shown on each side) are fixed. 
It will be evident that the electricity can only form a circuit when the thermometer 
is out of balance so that the platinum point at one end or the other touches that at 
the top of the corresponding pillar, in which case the wire attached to it, being in 
connection with the positive end of a battery, conducts the electricity from thence 
through the platinum points and along the metal plate under the scale of the 
thermometer, whence it escapes by the pivots into the two supporting pieces of 
brass, and passes into the pillar seen in front, and to which a wire is fastened 
leading to the earth, or negative end of the battery. 
The wires are led from the hothouse, where the thermometer is placed, to 
the gardener’s room, each of them being connected with a distinct-toned electric 
bell, so that, when the bell is rung by the means just explained, the gardener 
may know by its sound whether the house in question is too hot or too cold. The 
electric current may also be made to indicate the same facts in other ways. If 
the gardener’s house is situated at a considerable distance, one wire only, in order 
to save expense, may be used, but in this case only one bell can be rung. In 
houses where electric bells are already in use, the thermometer can easily be 
connected with them at very little expense. 
The tube of the thermometer is coiled round a central piece of wood on 
which the degrees are marked, and on this is placed a sliding weight and index, 
which, being passed along the top of the graduated scale, will balance the 
thermometer at the point indicating the particular temperature required. Then 
if the temperature of the house be equal to that at which the index is set, the 
tube will be evenly balanced, and no electric action will take place ; but if it 
becomes either too hot or too cold, the depression of the tube to the hot or cold 
end, as the case may be, will set up a current, and this will cause the bell to 
ring until the heat is regulated to meet the required standard. It has been 
found that in ordinary cases the instrument is too sensitive, to obviate which the 
centre of gravity may be elevated or depressed, thus making the action slow or 
sensitive, as may be required. This is effected by means of a screw fastened to 
the pendent beneath the tube. 
The action of the instrument is the result of the expansion of spirit, which 
occupies the upper part of the tube, and rests on quicksilver in the lower part. 
This latter, by the expansion or contraction of the spirit, is displaced at one end 
of the tube and driven over to the other, as the heat or cold may predominate. 
