T o mlinson 's Incub a tor. 
6 3 
is a question of common-sense and practical management. The Tomlinson incubator is shown 
in section in Figs. 37A and 37B. A is the case, enclosing packing shaded black, and projecting 
at one side over the lamp D ; C the water tank, also projecting over the lamp, and traversed by two 
or more hot-air flues ; E is a door for cleaning the flues without interfering with the machine ; F is 
the front of egg-drawer, with the thermometer-scale showing outside ; G is the egg-drawer, fitted 
with perforated zinc tray covered with flannel, underneath which are evaporating-pans for holding 
wet sand ; H H are openings in the bottom of the machine, doubly covered with perforated zinc, 
for admitting air to the drawer ; the air thence passes through small holes in the wooden bottom of 
the drawer, and thence over the moist sand, passing out through holes in the sides of the drawer 
into chambers hh, communicating with a vertical flue at the back, surmounted by the controlling 
regulator-valve L. The regulator itself is also lettered L in Fig. 377V ; but the valve is so set as to 
allow a certain minimum amount of ventilation at all times. 
The regulator of this machine depends upon the expansion of air, and is shown in Fig. 38. 
The glass tube shown in the figure is sealed at both ends, and has on the under side a cup-shaped 
opening, which is closed by a diaphragm or membrane of india-rubber tied tightly round its lip ; 
but before this is done the temperature is brought to about 90° Fahr., and a little water put in the 
tube, which runs down to the cup and keeps the joint air-tight. When the air expands, the 
diaphragm swells out and presses down the button at the end of the lever shown, and so lifts 
the valve connected with the egg-drawer, and allows hot air to escape. O11 the other hand, if the 
heat falls, the india-rubber bulges in, and the button rises and drags down the valve, which is never 
quite closed, but always allows a little air to escape. This regulator is liable to be somewhat 
affected by a very high barometer, which checks the expansion ; but under the conditions above 
stated it acts quite efficiently. 
Still later, Messrs. Christy and Co. have brought out their patent “ thermostatic ” incubator, 
which also works by the constant heat of a small lamp under a circulating boiler outside the 
machine. That the manufacturers and introducers of the hydro-incubator should have done this, 
is conclusive proof of the soundness of the views we have here expressed ; but this last incubator 
also contains several improvements in detail embodying more recent discoveries, which will be 
understood from the section in Fig. 39. The hot water tank, with the horizontal partition, is 
shown at U, and is fed by pipes R and R', from the small conical boiler II over the lamp S. 
The tank-bottom is, however, in 'his machine sloped round, so as to give a slight dome-shape 
to the top of the air or egg-cl amber, and from this ascends the air-shaft B capped by the 
regulator-valve A. All the air enters from the bottom by the apertures L I., as in Mr. Tom- 
linson’s machine, in doing which it has to pass through canvas, T, which dips all round into 
evaporating pans or troughs of water, and is kept constantly moist. Thence it passes through 
perforated zinc to the eggs. In this way the air is kept in free circulation, stagnation in 
the centre of the drawer being quite prevented, and it is unnecessary to change the places 
of the eggs, or do more than turn and cool them. The regulator Q is a thermostatic bar, 
