1866.] 



for regulating Temperature j ^c. 



145 



tube is filled, as also about half of each bulb, with mercury ; the lower 

 bulb containing ether to the depth of half an inch, which floats on the 

 mercury. The tube is secured to a plate of boxwood, and supported on 

 knife-edges, on which it turns freely. At the end of the plate, underneath 

 the highest bulb, is a lever, to which a string is attached. This string is 

 carried, by means of bell-cranks, to the supply-valve of a gas-stove, or the 

 damper of a furnace. 



The instrument acts in the following manner Supposing the stove to 

 be lighted and to have raised the temperature more than is required, the 

 heat will convert a portion of the ether in the lower bulb into vapour. 

 The expansion of this vapour drives a quantity of the mercury out of the 

 bulb underneath it through the tube into the upper bulb. The end to 

 which the mercury has been driven being thus rendered the heaviest falls, 

 and motion being communicated by the lever to the string, this closes the 

 supply-valve or damper of the stove or furnace. Of course, if this should 

 be carried beyond the required extent the reverse action will take place. 



A weight in the centre of the plate, the position of which is regulated by 

 a milled-head screw shown at the side, serves to alter the centre of gravity 

 of the whole apparatus. The value of the motion of this weight being 

 carefully ascertained, a scale is engraved upon it. By moving this weight, 

 according to a scale engraved on it, the instrument may be set so as to 

 maintain any desired temperature in the building in which it is fixed. 



The range of action of the instrument is from 54° to 66° Fahr., and 

 with a change of temperature of one degree it has the power to raise one 

 ounce three inches. 



Appolds automatic Hygrometer for keeping the Air in a Building at any 

 desired degree of moisture. 



This instrument, both in principle and construction, is very similar to 

 the automatic regulator just described. The acting portion consists also 

 of a tube with a bulb at each end. This tube contains mercury to about 

 half the height of each bulb, and a portion of ether floating on the mer- 

 cury at each end. One half of the tube and one bulb is covered with 

 bibulous paper, which is always kept wet, and the tube is suspended and 

 turns freely on knife-edges placed just above the covered bulb. The action 

 of the apparatus is as follows : — 



A deficiency of moisture in the air increases the evaporation from the 

 bibulous paper. This evaporation produces cold, which condenses the 

 vapour of the ether in the covered bulb, and the mercury being pressed on 

 by the vapour of the ether in the naked bulb is forced into the covered 

 bulb. The uncovered bulb, being now much the lightest, rises, and raises 

 a lever, which in its turn opens a valve at the end of a small tube. This 

 tube communicates with a cistern kept full of water. The water which is 

 thus admitted is suffered to trickle over heated pipes which are covered 



