72 



THE BOOK OF FOULTRY. 



cipal types of thermostats which have been 

 employed in incubator work. One of the first 

 to work efTficiently was that of Jacob Graves. 



Fig. 36. — Graves' Regulator. 



Here a large bulb or tube A L (Fig. 36) extend- 

 ing all along over the eggs in the chamber, was 

 connected by a neck-cork C with the tube M. 

 The tube A L was filled with alcohol, which 

 expands greatly when heated ; M was partially 

 filled with mercury, carrying the float or piston 

 F, which worked the lamp and valve, as it was 

 pushed by the expanding alcohol up the tube. 

 This regulator has been revived quite recently ; 

 a practically similar one being used in the 

 American " Reliable " tank incubator of the 

 present day. 



Mr. Halsted introduced the "balancing" 

 mercury regulator (Fig. 37). In this the bulb M 

 on the end of a sealed tube T was large enough 

 to hold about half a pound of mercury, of which 

 sufficient was introduced to extend to about the 

 shaded portion at 100°, the whole then balancing 

 on the axis A A. On the heat increasing the 

 mercury extended up the tube, when T descended, 

 the turning axis A A working the valve. The 

 whole was regulated and balanced by the weight 

 W, sliding on an arm L fixed to the axis. This 

 form was found awkward and cumbrous, and 

 regulation poor, while breakage of the bulb was 

 frequent ; but the balance principle has been 

 modified and used in many ways. In the best 

 examples, the balancing weight of the mercury 



^ig- 37- — Halsted's Regulator. 



is used in combination with the expansion of 

 much more sensitive liquids. One of the most 

 beautiful, sensitive, and really efficient balance- 

 regulators ever designed, Mr. Boyle's, is shown 

 in Fig. 38. The long limb A of a siphon-tube 



was in connection by the pipe B with the hot 

 water in the tank, which in his machine was the 

 medium regulated, the water extending nearly 

 to the bottom of the siphon : in modern 

 machines A would be connected with a long 

 bulb-tube in the drawer, precisely as in Fig. 36. 

 and might be filled with either water or alcohol. 

 C is filled with mercury, and connected by the 

 rubber-tube D with the small horizontal tube E 

 ending in a cup F, all which also contain 

 mercury. It will be seen that the expansion in 

 and behind A forces more mercury into the cup 

 F, and as the tube E is ten or twelve inches long, 

 and turns on D as a pivot, the increased weight 

 is added solely at the point where its leverage 

 is most powerful. The motion can be utilised 

 in any way by a thread or wire at M, and the 

 cup is connected with a lever H K, pivoted on I, 

 by which the action is balanced and regulated 

 through the sliding weight L. This regulator 

 works with a variation of one-tenth of a degree : 



Fig. 38. — Boyle's Regulator. 



it is in fact so sensitive, that it is advisable to 

 steady it somewhat by connection with a balanc- 

 ing spring G. On its own machine it was quite 

 thrown away ; but we know as the result of 

 experiments in other branches of biological 

 study, that it is one of the most perfect regulators 

 in action of any that have been devised, and 

 have often wondered that it has not been applied 

 to modern incubators, for some of which it is 

 well adapted. 



The expansion of mercury has also been 

 used to complete a battery circuit in what are 

 called "electric" regulators. We would warn 

 the reader to avoid all such, though the idea 

 seems to have fascinated a large number of 

 inventors. They are very sensitive in a way 

 — almost hyper-sensitive in fact, to a certain 



