an Improved Thermometer, 75 
the fmenefs of a hair, about five ievenths of an inch in length, 
which, being fet a little oblique, p relies lightly againft the ; 
inner fur face of the tube, and prevents the index from follow- 
ing the mercury when it defeends, or being moved by the fpirit 
palling up or down, or by any hidden motion given to the in- 
ftrument by the hand or otherwife ; but at the fame time the 
prelfure is fo adjufted as to permit this index to be readily car- 
ried up by the furface of the riling mercury, and downwards 
whenever the inftrument is be rectified for obfervation. To pre- 
vent the fpirit from evaporating, the tube at the end i is clofely 
fealed *. Fig. 3. reprefents the thermometer on its frame ; 
the plates on which the fcale is graved on either fide are made 
to hide out, and the frame is open to the back, behind the 
large tube, which does not touch it, except at each end. The 
cap a , and the bafe £, are made to fix on with ferews, and 
only cover the turning of the lmall tube. By a ferew at the 
bottom of the frame, it may be made fall; to the wall againft 
which it is to hang without doors, to prevent its being fhaken 
by violent winds. Towards evening I ufually vifit my thermo- 
meter, and fee at one view, by the index on the left fide, the 
cold of the preceding night ; and by that on the right, the 
heat of the day. Thefe I minute down, and then apply a 
fmall magnet to that part of the tube againft which the indexes 
reft, and move each of them down to the furface of the mer- 
cury : thus, without heating, cooling, feparating, or at all 
difturbing the mercury, or moving the inftrument, may this 
* when this tube is clofed (not hermetically, but only fo as to prevent the 
fphit s evaporating) the thermometer mull be brought to the greateft heat it is 
likely at any time after to fuMn ; and though no more air is incited than what 
remains at that time above the fpirits, yet that will, by its elafticity prefiing on 
the fluid, anfvver every purpofe as well as if the external air was freely admitted. 
T 2 ther- 
