72 GENERAL MANAGEMENT OF POULTRY. 



expands at the further end into the larger cup or bowl, p. 

 The mercury extends from the point where the expanding 

 water acts upon it to the bowl or cup, F ; and it will be readily 

 understood that as the water expands, and presses on the 

 mercury in the large syphon-gauge, it forces a portion along 

 the much smaller tube, E, and causes the fluid to rise in the 

 cup, F. The tube, B, being some ten or twelve inches in length, 

 the leverage and consequent power exerted by the weight of the 

 mercury in this cup are very considerable, and fully adequate 

 to any operation required for regulating, whatever may be the 

 heating power. The cup F is connected by a wire with the 

 lever, H K, moving on a fulcrum, i, and is carefully balanced 

 by a weight, L. To avoid the too sudden movement which 

 would otherwise occur with the least fluctuation of heat (for 

 this regulator is so sensitive as to move with less than the 

 tenth of a degree), it is also balanced by a spring, G. 



The superiority of this regulator over previous mercury 

 regulators is, that they depend upon the expansion of mercury 

 under heat, whereas this one works by the expansion of water, 

 which is many times as great ; while by that expansion acting 

 upon mercury, the greater weight of the latter fluid as a motive 

 power is also secured. It is this, combined with the long 

 leverage of the tube E, which makes the regulator so delicate. 

 It may be connected with the source of heat by a wire, chain, 

 or thread, M, in any desired manner. 



The incubator itself is arranged as follows : The eggs are 

 laid in oval holes in a plate, N (Fig. 15). A cold-water tank under- 

 neath supplies some moisture ; and more is given by wetting 

 portions of cotton- wool, which are placed in small holders, o, up 

 the centre of the egg-plate. Air is admitted pretty freely under 

 the egg-plate, which thus keeps the under-surface cooler than 

 the top, escaping by openings above. The rows of eggs thus 

 placed are ranged immediately under arches in the heating-tank 

 p, connected by a pipe, Q, .with the boiler. The eggs, as soon 



