82 



THE BOOK OF POULTRY. 



beneficial to the eggs. This also has been 

 experimentally proved, if only in a percentage, 

 although very good hatches have been obtained 

 without any such withdrawal. The turning 

 should be done deliberately and gently ; and 

 when so done, the eggs of a large machine are 

 generally best returned at once. But they may 

 be left outside for ten minutes or more in warm 

 weather, or five minutes even in winter, unless 

 the room be nearly freezing. Many have 

 advocated, and still advocate, leaving them 

 much longer ; but it is now known that such 

 " airing " has been much overdone, and that 

 where it has appeared beneficial, this was be- 

 cause it remedied in some degree the effects 

 of too much heat, or too much moisture. It is 

 manifest that in large hatching-chambers or 

 ovens the eggs get no cooling at all. ExceptK)n 

 may be made in hot weather, when "quickened" 

 chickens may add so much heat to the chamber, 

 that any valve may hardly be able to keep the 

 temperature down. We have known the thermo- 

 meter at 92" in the room, even in England; it 

 will easily be understood that in such a room, 

 and with lively " quickened " eggs, the smallest 

 flame possible may run the egg-chamber 

 up too high, and long, even repeated airings 

 will often at such times help the hatch. Mr. 

 J. L. Campbell records one extraordinary expe- 

 rience during a "heat-wave" in America, when 

 for five days and nights he had to take out his 

 egg-trays and keep them on a table, and the 

 eggs never got below 105°. But these are ex- 

 ceptions. The chamber should generally be 

 closed while the eggs are withdrawn, in order 

 that they may go back into nearly the proper 

 temperature. 



Not later than the sixth or seventh day 

 the eggs should be tested for fertility, and sterile 



ones taken out. This is more im- 

 Fertiufy.'"" portant than in natural hatching, 



owing to the difference already 

 mentioned between the heat of a live and of a 

 dead egg. This difference, when a large number 

 are collected, as in an incubator, becomes much 

 exaggerated. If the chamber is, upon the whole, 

 at the right temperature for live eggs, any live 

 eggs surrounded by dead ones will be insufficiently 

 heated. Moreover, a thermometer laid upon 

 eggs may appear to play all sorts of pranks. 

 For small occassional hatches, nothing need be 

 added concerning "testing" to what was said in 

 the preceding chapter; but the large or systematic 

 operator will find it worth while to use more 

 powerful appliances, and will very soon become 

 more expert, so as to be able to detect sterile 

 eggs on the third or fourth day. Brown-shelled 

 eggs are less transparent, and duck eggs more 



so than white hen eggs, so that many of the 

 duck-raisers can tell if an egg is fertile after 

 about thirty-six hours. In the first edition of 

 this work we figured an egg-tester with a 

 concave reflector behind the flame of a lamp, 

 and a lens in front, to condense the light upon 

 the egg; but at a later period, being asked by 

 a friend for optical advice * as to the most 

 powerful instrument that could be devised, we 

 designed one as in Fig. 48, whose effect in 

 bringing out the early stages is very marked ; 

 but whose efficiency depends upon the details 

 being optically correct. Here L is an oil-lamp 

 with an inch-wide wick, and R is a silvered 

 reflector, whose curve should be struck from 

 the centre of the lamp-flame. In front is a 

 lens C of 3i inches diameter and short focus, 



Fig. 4N. — Egg-Tester. 



such as is used in a magic-lantern condenser, 

 arranged at a little more than its focal distance 

 from the flame, so that it transmits the rays in 

 a slightly convergent beam, thus concentrating 

 them upon the egg E. Beyond the lens is a flat 

 mirror M, placed at an angle of 45 degrees, so as 

 to reflect the rays perpendicularly upward upon 

 the egg E, laid upon a proper orifice in a hori- 

 zontal screen. The efficacy of the instrument 

 depends partly upon all the rays taken up by a 

 rather large lens and reflector, being concentrated 

 into a space the size of an egg, and partly upon 

 the egg being laid horizontally to receive those 

 rays, so that the germ, lying close to the top side 

 of the egg, shall be more clearly seen. The egg is 

 also removed to a more comfortable distance from 

 the flame. Such an instrument would be put to- 

 gether to order by any respectable optician. In 

 using it, care should be taken to lay the egg 

 down in the same position in which it was 

 taken from the tray, in order that the germ 

 may be steady near the top side, nearest the 

 eye. 



When thus powerfully illuminated by a good 



* The author of this work will be known to some readers as 

 also the author of several upon " Light," and various branches 

 of practical and experimental optics. 



