THE PEOPLE'S PRACTICAL POULTRY BOOK. 157 



and provided for separately. The hot air chamber is provided with a u safety 

 valve," acted on by the expansion of mercury, which opens at a given tem- 

 perature. This valve seems to have been employed first by M. YALLEE of the 

 Jardin des Plantes, Paris. Mr. BRINDLEY'S valve seems to have been su- 

 perior to all those shown before him, and to answer all reasonable purposes. 

 Mr. WRIGHT thinks it impossible to make any valve the sole regulator, and 

 expect it to keep the heat uniform. He is under the impression that when 

 the heat becomes two or three degrees too high all that is expected is, that 

 the valve will open and admit cold air to reduce the temperature; but if the 

 air is really hot the valve, though open, cannot entirely keep the heat down, 

 nor can it guard against a lower temperature than is proper. We shall show 

 hereafter how the heat is regulated by the Graves' plan, so as to obviate 

 these difficulties. 



BRINDLEY'S machine diifers radically in principle from the preceding one, 

 MS also from Mr. F. H. SCHRODER'S, in that the valve is not employed directly 

 to warm the eggs but simply to impart heat to a chamber of hot air through 

 which the heat is communicated. In other respects the management is simi- 

 lar. The eggs require to be withdrawn and cooled once a day ; should be 

 carefully turned and sprinkled with warm water, which should also be allowed 

 to moisten the felt lining of the tray in which they are contained. 



THE INCUBATOR OF MR. F. H. SCHRODER 



is shown in figure 4. He has adopted an altogether distinct and separate 

 boiler, which is not shown ; but which is connected with the hot water tank 



FIG. 4. 



C, of the incubator by two pipes ; B being the inlet pipe, and D the outlet. 

 This tank is provided with, an open table, I, in which a thermometer can be 

 placed to show the temperature, and with a ventilating tube H, which is open 

 at top and bottom. Under the tank slide the egg drawers E, which in area 

 resembles the quadrant of a circle this is of a circular form. 



