442 Mr BLACKADDER'S Description of a Register Thermometer. 



evaporating fluid is kept applied to their bulbs. The existing 

 atmospheric temperature was supposed to be 60 ; let it now be 

 supposed that the loss of heat caused by evaporation is equal to 

 ten degrees. The mercury in the tube a will then point to 50, 

 and that in the tube d to 10 on their respective scales ; and then 

 10 + 50 60, which was the temperature of the air at the in- 

 stant the globule quitted the open extremity of the tube d, when 

 the instrument received its horizontal position. 



The way in which the instrument may be placed in a hori- 

 zontal position, at any given instant during absence, was former- 

 ly described, a pocket time-piece, and a small additional but 

 simple piece of mechanism, being ah 1 that is requisite. A vessel 

 for containing the evaporating fluid, fitted with a valve, and a 

 capillary tube terminating in one or more small and soft hair 

 brushes, Fig. 4. completes the apparatus, and which can obvious- 

 ly be made of such small dimensions as to be easily portable. 



If the bulb at the upper extremity of the tube rf, Fig. 1, be 

 made of the bent form represented in Fig. 3, the instrument does 

 not require to be moved from a horizontal position. In this 

 case, the globule of mercury is made to quit the open extremity 

 of the tube </, and fall to the bottom of the bent bulb i, Fig. 3, 

 by the tube d, on a separate piece of ivory, being made to turn 

 half-way round on itself, the centre of motion being a line drawn 

 through the centre of the tube, and the extremity of the bent 

 portion being thus made to describe the half of a circle. Or, 

 both tubes may be attached to one slip of ivory, and the latter 

 be made to turn half-way round its own centre, being suspended 

 at each end, so as to admit of that motion. 



This semirotation can readily be communicated at any given 

 instant, by the assistance of a time-piece, and a very little addi- 

 tional mechanism. 



It is perhaps unnecessary to add, that this registering ther^ 

 mometer may be used as an Atmizomic Hygrometer. 



