66 
The Illustrated Bools of Poultry . 
anywhere from g8° to 107°, and will afterwards, whatever the variation in outside temperature, 
keep the heat regular within about two degrees. The only exception would be in any unusually 
high situation, which, owing to the less barometrical pressure, would require an ether prepared 
accordingly ; and in several instances this has been found to be the case, but a special capsule 
has at once removed the difficulty. From numerous sources we learn that the incubator thus 
designed and regulated has hatched with almost unvarying regularity and success. 
In 1886 an incubator on another principle was brought out by Mr. W. H. Hillier, of Nails- 
worth, which dispenses with any tank at all. The lamp is placed under an open central flue, 
through which the heated air, mixed with ordinary atmospheric air, passes direct into a large 
central chamber open at the top, over the side-walls of which it flows direct into the surrounding 
e gg-chamber. The eggs are laid on perforated metal, and there are free ventilating holes at 
top and bottom of the chamber always open. The lamp gives always a surplus of heat ; and the 
regulator, which depends upon a small quantity of ether pushing forward a column of mercury, 
operates by closing a damper which controls the entrance of the heated air from the lamp. A 
vessel of water in the flue over the lamp keeps up a moist atmosphere. In spite of the entrance 
of the products of combustion into the egg-chamber, this incubator is reported as hatching ex- 
ceedingly well, and gives very little trouble in management. 
Such are the most successful British incubators lately constructed, and only a few general 
remarks need be added. In artificial hatching, it is of great importance that the eggs be fresh. 
The earlier incubators rarely hatched any eggs laid more than three days before putting in the 
machine. The modern ones here described have often reported successful hatches of eggs laid 
a fortnight before, and which have also travelled by rail ; and no greater proof can be given of the 
advance attained. But every pains should be taken to give the machine a fair chance in this 
respect ; and one modern discovery should receive special attention, though of importance to all 
poultry-keepers. The risks of “ travelled ” eggs, and their uncertainty of result, are well known. 
But it has been recently established by careful experiments, often repeated, that if after a journey 
one-half the eggs be “ set ” at once under a hen, while the rest are kept still and free from jar for 
twenty-four hours, on an average those kept hatch much the best. It appears that even the un- 
developed germ, by virtue of the principle of life implanted in it, has some strange power of 
resting, or recovering through rest injuries of this kind. It may also be noted that eggs of 
water-fowl are on the average easier to hatch than those of fowls, but require a very free supply 
of moisture. The practical details of management have been sufficiently treated in describing the 
hydro-incubators. 
Of late there has been, owing to high breeding, a marked decline in the average fertility of 
eggs from “ fancy ” stock. Hence the eggs of cross-bred fowls hatch much more readily than 
others, as a rule, and an incubator may often be used with great success on a farm, where poultry 
are bred for market, when less successful with the fancier. This decline in stamina is to be 
regretted and ought to be mentioned here ; but recent reports have gone to show that the most 
approved makes of incubators have fully equalled hens in average performance (in winter and 
early spring considerably surpassing them) when in intelligent hands. 
In this chapter we can perhaps most properly mention the hatching by means of hen turkeys, 
as carried on in France by the couvcurs or professional hatchers, differing as it does considerably 
from the natural mode of procuring chickens. The best description of this method of manage- 
ment is contained in Mr. Geyelin’s report to the Directors of t! e then existing National Poultry 
Company, and dated July, 1865. “ The hatching-room is kept dark, and at an even temperature 
