6 4 
The Illustrated Book of Poultry. 
similar in principle to that already described in Mr. Renwick’s machine, or to the balance of a 
45 compensated ” watch. If two strips of different metal are riveted together, cne of which expands 
with heat more than the other, it is obvious that, when both are heated, the one which expands 
most must curl the other more or less, that it may find room for its own expansion at the cir- 
cumference of a larger or outer circle. The principle is of constant application in mechanics. 
With heat, therefore, the free end of the bar Q curls downwards somewhat, and thus pulls down 
the end, D, of a lever which raises the valve A, and lets out warm air. C is an adjusting screw to 
set the valve, and F merely a wire-cage to protect the regulator from injury. N is the ther- 
mometer, O the lamp reservoir, and P a sliding shelf which pushes up the lamp towards the boiler 
Fig- 39- 
and chimney. In these machines the lamps should be trimmed every twelve hours, always 
turning the eggs first, before this is done, to keep them from the smell as much as possible. 
The open pipe F (which is advisable to prevent explosion in all lamp incubators, and is also 
necessary for the insertion of a thermometer into the tank) should be filled up with warm 
water every other clay, and about the same number of times the evaporating pans will need 
refilling, for which luke-warm water should be used. Otherwise the general management 
will be much the same as before described. 
While, however, we have thus seen the great desideratum of uniform temperatuie (and 
consequent evaporation) secured by comparatively simple means, it will be obvious that the same 
result might also be secured by a more perfect regulator. Mr. Boyles machine hatched well, if 
breakages were avoided, in the hands of those who could master its complicated mechanism , and 
it only remained to devise a more simple regulator, which should be equally or more effective, and 
should work from the egg-drawer, to attain the desired object. This has been attained by 
Mr. IJearson in his regulator, which depends for efficiency upon the fixed boiling-point of a fluid. 
