CARE OF THE EGGS. 291 



lamp by dropping a thin, very light, circular metallic 

 plate over the top of the chimney, or by turning down 

 the wick or shortening it by a sliding tube, the method by 

 lessening the draft being preferable because needing 

 less power and therefore being more delicate and certain 

 in its working. Now here we approach a difficulty. No 

 matter how perfectly the heat regulator works there 

 must still be some change of air or it will become 

 impure, because the eggs exhale a poisonous gas, carbon 

 dioxide or carbonic acid gas, when the embryos are 

 growing, too much of which gas in the egg chamber 

 would seriously impair or utterly ruin them. 



Now, as the temperature of the air will vary outside 

 the incubator, and the moisture it contains differs widely 

 in different parts of the country, and at different times 

 and seasons in the same section, it is evident that no 

 hard and fast rules can be set for supplying moisture. 

 Each operator should obey the instructions given by the 

 manufacturer for the use of his machine, remembering 

 that the admission of air to the eggs in cold weather or 

 very dry weather will evaporate moisture from them 

 faster than when the air is warm or damp outside. For 

 it must always be kept in mind that warming a volume 

 of air increases its thirst, as we may say ; that is, it 

 increases its affinity for moisture and makes<it drink 

 from the most available source of supply from moisture 

 pans or wet sponges if they are present, or if not, from 

 the eggs. The only way to success is to use your rea- 

 son. If you change the air but little and slowly, as the 

 hen does, and ir there is summer weather or mild spring 

 weather, or if the locality itself is a moist one, as on a 

 damp seacoast for example, or if the location is moist, a 

 damp cellar for instance, you will need to have but little 

 water in your incubator, or none at all, and everything 

 will be all right so far as moisture is concerned. On 

 the other hand if the weather is cold, or rather if the 



