THE HYDRO-INCUBATOR. 



69 



as shown at the left hand of the figure (the 

 top ring R being a drying box for the chickens). 

 The eggs were placed in rows in the apertures 

 of a perforated plate, N, so that when pushed 

 into place the rows of eggs were almost 

 touching, and enveloped by, these arches. At 

 O were small receptacles for holding wetted 

 cotton wool. The bottom of the plate and 

 eggs in it were exposed to the air. With 

 this system of top heat, and the bottom sides 

 of the eggs cool, it was found that the re- 

 quisite temperature was about 106°, whereas 

 in a drawer warm all through it is about 

 103°. This distinction is important, as will 

 presently be seen. The arrangement was, 

 however, awkward in practice, breaking eggs 

 wholesale in sliding the egg-plate in and out; 

 and though Boyle's machine hatched well on 

 many occasions, it never came into general 

 use. 



American incubators, during the same 

 transition period, had more general similarity 

 in design. Patents were taken out by dozens, 

 but we can find little of value. In 1S70 Jacob 

 Graves and Co., of Boston, introduced an in- 

 cubator whose type lasted many years, and 

 did much work. It embodied Schroder's cold- 

 water tank under the eggs, with a hot-water 

 tank over them, and a chicken nursery or 

 drying box on top of all ; and its regulator 

 acted by the expansion of alcohol in two 

 large tubes extending through the egg-chamber 

 (see Fig. 36). Mr. Halsted introduced an 

 arrangement of flues through the tank which 

 tended to make the water rather hotter round 

 the edges than at the centre, thus counter- 

 acting the too great heat in centre of the egg- 

 drawer, which was and is still found a general 

 defect. He also introduced the regulator whose 

 type is mercury expanding by heat, and so over- 

 balancing a lever and working a valve (Fig. 37). 

 This being faulty, he abandoned it for a com- 

 pound thermostatic bar, and with this and some 

 other modifications, his machine had a sale 

 during many years as the Centennial. The 

 most original idea we have come across in older 

 American machines was that of Mr. E. S. Ren- 

 wick, whose system radically differed from others 

 in not attempting to keep the temperature uni- 

 form, but aiming rather, after maintaining it at 

 a miuiinum for some hours, then to raise it to a 

 maxivmm of about three degrees higher. This 

 was done by a clockwork arrangement. There 

 is no doubt that this remarkable machine 

 hatched well, but it was too complicated and 

 costly for popularity. So far as we are per- 

 sonally aware, the same inventor seems the 

 first to have formed the bottom of the egg- 



drawer of rollers, by whose revolution the 

 entire drawerful of eggs could be "turned" at 

 one time. Those here mentioned were all tank 

 machines, which prevailed for many years as in 

 England; only by degrees being manifested that 

 preference for the hot-air system which dis- 

 tinguishes the best American machines of the 

 present day. 



Such was the state ol affairs at the com- 

 mencement of the last quarter of the nineteenth 

 century. The prominent importance of uniform 

 temperature (for even Mr. Renwick's systematic- 

 ally varied temperature was to be within defined 

 uniform limits) had been recognised ; but that 

 object had not been really attained by the 

 regulators then in use. Some of these, es- 

 pecially in America, had been carried to the 

 extreme of elaboration and apparent efficacy ; 

 still they failed to do their work. That moist- 

 ure and ventilation also played an important 

 part was known, but not well understood, not 

 especially the relation between them ; and there 

 is no doubt that some of these older incubators 

 would give good hatches now, handled with the 

 knowledge since acquired respecting these latter 

 points. What artificial hatching was done was 

 chiefly in America ; where the popularity of 

 Leghorns and broiler chickens made it more 

 necessary, where the number of incubators pro- 

 duced skilled operators, and where regulators on 

 an average surpassed English models, though 

 still leaving a great deal to be desired in their 

 operations. 



Strange to say, artificial incubation became 

 a practical reality in England owing to the in- 

 troduction by Mr. T. Christy, in 

 S'cubltor"" 1 877, of a machine of the rudest con- 

 struction, known as the Hydro-In- 

 cubator, made upon a model already successfully 

 used in France. The heater was a large rect- 

 angular tank of water, from the upper portion 01 

 which was withdrawn every twelve hours a cer- 

 tain number of gallons (variable according to 

 the thermometer indications), to be replaced by 

 boiling water, thus keeping up the temperature. 

 Under this tank was the egg-drawer, provided 

 with arrangements for damping and apertures 

 for ventilation, the whole being surrounded by 

 non-conducting material. There was a ther- 

 mometer in the tank and another in the egg- 

 drawer ; literally nothing else. 



When so many had vainly devoted money, 

 pains, and complicated apparatus to main- 

 taining a uniform supply of heat, that a simple 

 machine should succeed which depended alto- 

 gether upon a re-supply of boiling water every 

 twelve hours, appeared to all simply ridiculous, 

 and it was some time before it was understood 



