70 



THE BOOK OF POULTRY. 



why it was that such success had attended so 

 rude a contrivance. Mr. Christy himself thought 

 the reason to be that there were no lamp-fumes 

 near the eggs, an idea long since exploded by 

 machines which admit such fumes directly into 

 the egg-chamber. The secret really lay in 

 two points. In the first place, the hot-water 

 tank was very large compared with apparatus 

 previously made, holding for a lOO-egg machine 

 about twenty or twenty-four gallons. The enor- 

 mous " specific heat " of water makes a large 

 body of it very " steady " in temperature. But 

 the construction of the tank was also peculiar. 

 If we take a flask of water containing a few 

 particles of bran, and apply a lamp to the 

 bottom, we shall see how the 

 heated water rises and circu- 

 lates, and the whole becomes 

 quite hot in a very short time. 

 But if we apply a hot plate 

 to the surface of the water in 

 an open glass vessel, there is 

 scarcely any movement, and it 

 is a long time ere the heat 

 reaches the lower portion of 

 the fluid. This time may be 

 increased still further by hori- 

 zontal partitions, which compel 

 the hot water to take a round- 

 about course. The tank in 

 the hydro-incubator was not 

 only large, but furnished with 

 such partitions ; and the boiling 

 water was always supplied at 

 the top. Thus the heat per- 

 colated very slowly downwards ; 

 and while the water drawn off 

 (from three to six gallons) 

 was generally about 146*^, and 

 replaced by water at 212'^, the temperature of 

 the bottom layer, which acts upon the eggs, 

 only varied in a small degree, and that in a 

 regular manner within certain limits, which 

 might be actually beneficial to the eggs, ac- 

 cording to Renwick's theory above mentioned. 

 Hydro-incubators were sold by scores, and 

 artificial hatching in England became at once 

 a practical success. With this, valuable ex- 

 perience was rapidly accumulated, followed by 

 improvements in details of management. Its 

 work being done, however, the hydro-incubator 

 itself only remained in use for a few years. 

 Simple as the system was, the provision of 

 gallons of boiling water every twelve hours was 

 found such a tax, that there was a demand on 

 all sides for supplementary apparatus. The 

 further step was soon taken of carrying circulat- 

 ing pipes from a small boiler into the tank of 



the machine ; and instead of replacing from 

 three to six gallons by boiling water, every twelve 

 hours, at the same periods, the lamp under the 

 boiler was lit for a short time. Finally, however, 

 manufacturers have returned to the old system 

 of employing the constant heat of a lamp. 



The incubators now in use are constructed 

 upon two systems, known as the " tank," and 

 "hot-air " or"atmospheric"systems. 

 In England the tank system has 

 generally prevailed, owing partly to 

 the sudden success of the hydro 

 system above described, but more 

 recently to the excellent results of the incubator 

 and regulator patented by Mr. Hearson in 



Hearson's 

 Incubator and 

 Capsule 

 Regulator. 



November, 18S1. The earlier tank machines 

 were made with large tanks, often with hori- 

 zontal partitions on the hydro-incubator plan, 

 which "steadied" the temperature, and gave 

 fair results with very mediocre regulators ; the 

 regulator in Tomlinson's machine, for instance, 

 acted by the expansion of heated air. With 

 better regulators, smaller tanks sufficed ; and 

 in fact Mr. Hearson somewhat reduced the 

 depth of his tanks as experience was gained. 

 The present form of this machine is shown in 

 F'to- 35- The tank A a, which is not intended 

 to be kept quite full, is traversed by the flue 

 LL from the lamp T. This flue is shown for 

 clearness leaving the machine at W, at the end 

 opposite the lamp, but really returns to the 

 same end before emerging. The top of the 

 lamp-flue or chimney V is covered by the valve 

 or damper F, so that when this is closed the 



