HOT-AIR AND TANK MACHINES CO AI PA RED. 



77 



Mr. Sutclifte's comparison just quoted ex- 

 plains the matter very clearly, and we may 

 here remark that in America the hot-air system 

 is far the most in use. One reason for Ameri- 

 can preference of the hot-air type appears to 

 be greater economy of oil, which on a large 

 scale becomes of importance. The latest and 

 best makes of these machines are able entirely 

 to dispense with moisture, and thus register 

 real advance. Almost universally they em- 

 ploy efficient metallic thermostats, which do 

 not vary with the barometric pressure, as do 

 Aose which, depending on vaporisation, are 

 liable to several degrees of fluctuation indepen- 

 dent of outside temperature. 



From the British Isles we have so far re- 

 ceived the best averages of reports from tank 

 machines, whose popularity we have seen to be 

 connected with the simplicity and uniform 

 action (within certain limits) of Hearson's cap- 

 sule regulator. It has been shown how a 

 tank of water steadies the temperature, acting 

 as a fly-wheel ; so much so that even if a 

 lamp should go out, the heat might probably 

 remain sufficient for hours to prevent fatal 

 results. These machines thus possess more im- 

 munity from catastrophes caused by accidents. 

 On the other hand, they respond much less 

 quickly to sudden changes of temperature, 

 while specially sensitive to changes in the baro- 

 meter, and are thus more liable to failure from 

 weather conditions. If it be remembered that 

 at the best there must be some variation in tem- 

 perature at different parts of an egg-chamber, 

 a possible variation of 3° or 4°* from baro- 

 metrical changes alone may become a very 

 serious thing, especially in the early stages of 

 hatching. Many such variations which occur 

 are never suspected. We have in our own early 

 experiments often supposed that the heat in 

 the comparatively rude apparatus we were then 

 using was within 2° of variation, because we 

 found it so at periodical morning and evening 

 inspections ; but when we put in a certified 

 registering thermometer, we found that the 

 variation under the same arrangements had 

 really amounted to as much as 6°. Now some- 

 times this effect of the barometer upon the 

 capsule may be actually beneficial. Suppose 

 pleasant cool weather with a high barometer, to 

 be followed by a rapid fall, with sultry heat and 

 a storm. Then the lower vaporising temperature 

 will the more easily and rapidly adjust matters 

 in the egg-drawer. But imagine cold and raw 

 but rainy weather, with a low barometer, in 

 spring, to be followed by bright, hot weather. 



* Mr. Willan's register for thirty-two days, published in Messrs. 

 Hearson's pamphlet, shows a variation from 102" to I06;<°, or 4'X'-'. 



As a result, the heat would run dangerously 

 high, and the chicks, if at an early stage, be 

 probably killed. Thus it will appear that a 

 capsule thermostat must not be left to work 

 unchecked, but that a barometer or aneroid, and 

 a thermometer for the room itself, should 

 always be used with a machine of this class. 

 The matter is of the more importance, as it will 

 be seen in Chapter VIII. that variation in tem- 

 perature is directly connected with incomplete 

 absorption of the yolk by the hatching chicken. 



The hot-air machine responds much more 

 quickly and sensitively to changes of tempera- 

 ture, and with good thermostatic regulators is in- 

 dependent of the barometer, and really automatic 

 in action ; with, however, the proviso that in 

 cool-bottom machines there be a double-acting 

 regulator, as explained above. On the other hand, 

 in the case of hot-air machines a neglected lamp 

 or flue must spell disaster, and it obviously 

 requires a more accurate and sensitive thermostat 

 or constant attention. Neglected lamps are 

 not to be dreaded in large systematic establish- 

 ments : the smaller breeder must judge for 

 himself whether he can trust his own careful- 

 ness, or whether he prefers the safety-valve 

 (in this respect) of a tank machine. 



Coming now to the practical working of an 

 incubator, any reader of intelligence will have 

 already gathered that in different 

 Management niachines details of management 

 Incubator. may differ considerably, according 

 to the construction, even in really 

 important points. No better advice can there- 

 fore be given than that, before starting, the 

 instructions sent with the particular incubator 

 in use should be carefully studied and fol- 

 lowed. The manufacturer is supposed to 

 understand the proper conditions for working 

 his own machine ; and though we regret to say 

 that in the case of some productions this is not 

 the case, as regards those which have held a 

 market it generally is so. In regard to choosing, 

 it will be well to confine the choice to some 

 make which has held its -position for three years. 

 We may say that so far, of every English 

 machine that fulfils this condition, we have had 

 ample evidence of good results when carefully 

 managed. In America such a rule would be 

 too stringent, excluding, perhaps, some good 

 machines ; but there the immense scale of oper- 

 ations, carried on by men whose names are 

 household words, gives an amount of testing in 

 a short time which is equally effective. It is 

 simply the amount of experimental proof, in 

 either case, which the purchaser has to consider. 



Where the incubator or incubators are to be 

 placed should receive consideration. Constant 



