■S c hr Oder’s Incub a tor. 
53 
immersion of the thermometer in the tank, or source of heat, instead of being where it should be, in 
the drawer or chamber which is heated. In the light of recent experience, as seen further on, it 
will also be seen that the hot-water tank was far too small. 
In 1866 Colonel Stuart Wortley, at that time an enthusiastic fancier, constructed an incubator 
on another principle. A saddle-backed boiler, furnished with a dome to collect all steam, and a 
supply cistern by which the height of the water was kept uniform, kept water circulating at a 
boiling, and therefore almost uniform temperature, through the pipes which heated the egg-chamber. 
These pipes passed through holes furnished with spring-pads to keep them air-tight, and hence by 
pushing in more length of pipes there was greater heat given for cold weather, or by withdrawing 
them a little the temperature could be reduced. The difference between this plan of heating and 
others will readily be seen ; it gets rid of any variation so far as the lamp or other source of heat is 
concerned, as the laws of nature give a uniform temperature of 21 2° for boiling water at the 
Fig. 29. 
ordinary pressure of the atmosphere. This is a great point, and changes of temperature are then 
guarded against by giving more or less of heating surface. The difficulty of providing a 
regulating-valve will readily be seen by all skilled mechanics, but, we think, might be overcome; 
and it seems to us rather singular that the method should have been never carried any further. 
An incubator sold by Messrs. Jacob Graves and Co., of Boston, U.S., is shown in perspective 
in Fig. 30. At the bottom is a cold-water tank, as in Schroder’s machine, and above this is the 
hatching-chamber heated by the hot-water tank. Above this again is an air-chamber, for retaining 
or protecting the heat required ; and on the top of all a drying-loft or nursery, F, where the 
newly-hatched chicks are placed after birth until removal to the separate “mothers” provided 
for them. The mechanism of the incubator cannot be explained without constant reference to 
the diagram. The lamp G heats the boiler H, which latter communicates by tubes with the 
hot-water tank. J J in the perspective view are simply reservoirs which supply oil to the 
lamps. Under and in contact with the heating-tank run two glass tubes filled with alcohol, 
each of which at the outer end communicates by a bent tube, L, with a cylinder, M, con- 
taining mercury, and which is furnished with a piston-float and rod, N. When, therefore, 
the temperature ' of the tank rises above that for which the valve is adjusted, the expansion 
of the alcohol in the tubes, acting on the mercury in the cylinder M, forces up the piston-rod N. 
The upper end of this rod is attached to a lever, O, which is pivoted on the machine, but 
