TEMPERATURE OF THE INCUBATOR. 



79 



The incubator should be carefully levelled. 

 This is essential to the lamp-flues working 

 properly, whether through a tank or a hot-air 

 chamber ; and a difference of level will in many 

 machines make one corner of a drawer hotter 

 or cooler than the others. Where it can be 

 done, it is worth while to equalise the tempera- 

 ture by placing a test-thermometer- in each of 

 the four corners of a drawer. Prospectuses may 

 state that the heat in their machines is so 

 " uniform " that the eggs do not need any change 

 of position. We have not found it so. Far 

 more usually the back corner next the lamp is 

 hottest, next the other back corner, then the 

 front corners in same order. Each machine 

 seems to have its own peculiarities, and by 

 propping up one corner or end a little, where 

 the construction admits of this, a drawer may 

 often be more nearly equalised, though no 

 machine has ever yet been made in which the 

 heat is uniform all over the drawer. It is un- 

 fortunate that all incubators are not made 

 with glass doors, or even separate doors to be 

 closed when the egg-trays are withdrawn for 

 cooling. In America nearly all of repute are 

 thus furnished, and this detail not only facilitates 

 the adjustment here described and examination 

 of thermometers, but saves much loss of heat at 

 the periods when the eggs are attended to. We 

 should, in fact, advise that any incubator not 

 already furnished with a separate outside door, 

 to be closed when the drawer is taken out, should 

 have a caulking shield or lid provided to fit into 

 and stop up the opening, and so confine the heat. 



In regard to temperature, it will follow from 

 what has been said, that no positive figure can 

 be given, even for one kind of eggs — 

 Temperature, we here suppose hen's eggs. Both 

 the figure, and the best place to pu 

 the thermometer, will differ with the machine ; 

 and the place of the thermometer will affect the 

 figure. In some top-heat machines which are 

 freely cool at the bottom, a quarter of an inch 

 lower for the thermometer bulb will make it 

 read one degree lower for the same heat of the 

 drawer. Thus it is that Mr. Hearson, with his 

 thermometer higher than the top of the eggs, 

 gives as the proper heat 104° for an outside 

 temperature of 60°, while 1° has to be allowed 

 for about 10° outside temperature in order 

 to keep the bulk of the egg itself at the same 

 heat, according to the warmer or cooler bottom. 

 It must never be forgotten in machines of this 

 class not to leave all to the regulator, but 

 to adjust the latter according to outer cond; • 

 lions ; and this is a very good instance of the 

 need for following special directions, which 

 may not apply at all to some other machine. 



A usual practice is to lay a thermometer on 

 the eggs, taking care after the tenth day or so 

 that it lies upon live eggs. In this case 102° 

 will be about the right heat for the first week or 

 so, corresponding in average machines to about 

 99° at bottom of the tray. But where this 

 system is followed, it is most important to bear 

 in mind that about the ninth day the life of the 

 chick begins to quicken, and after the eleventh 

 day to add a great deal of its own animal heat 

 to what is supplied. Hence, after the tenth or 

 eleventh day a thermometer upon a live egg 

 may run up to 105°, without the heat in the 

 drawer being really more than about 103°, 

 whereas if 105° were shown upon a dead egg, 

 the heat would be too great. For this reason 

 the more recent and better practice is for the 

 thermometer not to rest on eggs at all, but to 

 be in one fixed place, with the centre of the 

 bulb level with the top of the eggs. The 

 temperature for hen-eggs will then be about 

 103° for machines with decidedly cool bottom, 

 or 102° for machines where the heat is more 

 evenly diffused in the egg-chamber. In either 

 case the thermometer may probably register 

 about one degree higher after ten or eleven 

 days, owing to the greater heat and proximity 

 of the quickening eggs ; but this is about as it 

 should be in hatching, and is no fault of the 

 regulator. As it has been well expressed, while 

 for the first ten days the temperature of the 

 egg-chamber controls that of the eggs, after 

 that, to some extent, the temperature of the 

 eggs controls that of the chamber. 



The differences in temperature given by 

 various operators will now be understood, as 

 depending upon differences of level 

 Thermometers, or in machines. Statements that 

 only machines with " top heat " will 

 hatch successfully are mis-statements. The 

 egg-ovens of Egypt, as well as certain in- 

 cubator experiments, show their absurdity. 

 Top heat, or all-round heat, or bottom heat will 

 all hatch, if the heat be right. But the very 

 best thermometers commercially obtainable also 

 differ somewhat. In the early days we noted 

 many which differed four degrees, to which alone 

 many disasters were due. Even now many 

 differ half a degree or one degree, and this should 

 be allowed for as verified by comparison with 

 one tested and old thermometer kept for a per- 

 manent standard ; for it does not seem generally 

 known that even a' well-made thermometer, 

 accurate when new, will often show a rise of 

 from half a degree to a whole degree, or even 

 more, when it has been in use twelve months, 

 the first six months being most apt to show such 

 changes. For this reason, in America it is now 



