204 Report on Miscellaneous Implements at Newcastle. 
so tliat whenever tlie little capsule is brought to that tempera- 
ture the volatile fluid within it becomes steam, whose pressure 
causes the flexible walls of the thermostat to bulge like an 
india-rubber cushion when inflated. Mixing a little spirit of 
wine, which boils at 173°, with the ether will, of course, 
increase the temperature at which the " boiler" begins to bulge, 
and, indeed, the contained liquid should be one that boils at, or 
about, the temperature which the thermostat is designed to 
preserve. 
The woodcut illustrates the action of this simple device when 
applied to an incubator. 
Fig. G. — Ilearson's lliermostat. 
S is the Tliermostat. O, a rod the lower eml of which rests on the flat 
surface of S, while its upper end touches the underside of the lever G, 
which is hingod at P. and from whose farther extremity depends the damper 
F. L is a flue, passinf^ throunrh a water vessel occupyinj^ the upper part of 
the chamber to he heated, while T is a lamp, havinp: a chimney, V, closed 
by the damper F. It is evident that the amount of hoat passing from the 
lamp through the flue, L, would be determined by the position of the damper. 
When this was lowered, all, and, when raised, almost none of the lamp 
heat would take the course in question. Now the damper, F, is under the 
control of the capsule S ; when this expands it is lifted, when it contracts 
it is lowered, and in this way the temperature of the chamber is kept 
steady at, or about, the boiling-point of the liquid contained in the Tliermo- 
8tat. Adjustments of tliis temperature may, however, be made by means of 
the sliding-woight, II. 
