56 



The Illustrated Book of Poultry. 



When, therefore, the temperature of the tank rises above that for wliich the valve is adjusted, the 

 expansion of the alcohol in the tubes K K, acting on the mercury in the cylinder M, forces up the 

 piston-rod X. The upper end of this rod is attached to a lever, O, which is pivoted on the machine, 

 but moves freely at the outer end. Above, the free end of the lever is connected by a rod, R, with a 

 valve, P, and below by a spiral spring, V, with the lamp G. When, therefore, the piston is raised, the 

 valve P opens, and warm air rushes out to reduce the temperature ; while Q is a slide at the bottom 

 of the tube W to lower it still faster if so high as to make this necessar)-. At the same time this is 

 being done the lamp-flame is being lowered by the ingenious mechanism shown in Figs, n and 34, 

 which are enlarged views of the burner and its appliances. The lube or wick of the burner is shown 



I'"ig- 34- 



at s, and its orifice is beveled off at an angle. A little way off is pivoted on the shaft / a mov- 

 able leaf or regulator, T, which in ordinary stands away from the wick, but is capable of shutting 

 down close upon it, as seen at Fig. 34. From the end of the shaft / projects the lever U, to which 

 is attached the spiral spring V as already described. By. means therefore of the lever O and spring 

 V, at the same time the hot air is allowed to escape by the opening of the valve P, the lever U is 

 raised and the lamp-flame lowered by the shutting down of the flap T upon the tube of the burner. 

 It should be mentioned that the wire R is not rigidly connected with the valve P, but has a sliding 

 attachment, by which means the lever O is permitted the needed play even when the valve is closed 

 or opened to its fullest extent ; and also that the regulator T in Fig. 34 is adjusted so that the lamp 

 can never be entirely extinguished, though it can be graduated from a full flame to a scarcely 

 perceptible one. We may also say that all these parts are duplicate, there being a precisely similar 

 lamp, boiler, valve, and other contrivances at each end of the apparatus, one of the tubes K in Fig. 

 32 communicating with each ; and these two sets of heating and regulating apparatus to some 

 extent correct and compensate any sudden irregularities for each other, and make the total effect 

 more perfect and uniform. In fact, the Graves' incubator bears the character of being a thoroughly 

 good machine, though in one or two respects we do not consider it equal to the improved model 

 finally adopted by Mr. Ilalsted himself, and which is probably the most perfect apparatus yet 

 constructed, though even in it we think some minor improvements might be made. 



An outside view of the improved Halsted incubator is shown in Fig. 35. B is the boiler, 

 heated by a lamp in the usual manner, oil for the lamp being supplied from the reservoir O. The 

 lamp may be formed ot any convenient material, and is in the apparatus from which the 

 illustrations are taken of the German student-lamp pattern, but may be of any good construction 

 which will burn equally. Only the best oil or other fluid must be used, or the wick will rapidly 

 become so crusted that it will scarcely burn, and the heat of course fails. For this reason gas is 

 manifestly preferable, where it can be obtained free from the danger of being cut off without warning. 



