TEMPERATURE REGULATORS 



59 



cally sealed box, there would be very marked differences of temperature at 

 different levels, and the larger the incubator the more noticeable would 

 this be. [In very large incubators, such as incubator rooms, it is even 

 necessary to have thermometers on each shelf and at different places on each 

 shelf, because the differences of temperature in different parts of the room 

 are so considerable.] Hence to maintain as uniform a temperature as possible 

 in an incubator of the ordinary size the shelves are perforated with holes 

 to allow of free circulation of the air, and in some forms ventilation holes are 

 provided in the floor and roof. [With incubators surrounded by a water 

 jacket however this is not necessary.] 



SECTION I. DEVICES FOR AUTOMATICALLY REGULATING THE 

 TEMPERATURE OF INCUBATORS. 



Various ingenious pieces of mechanism have been devised for the purpose 

 of automatically regulating the temperature of incubators. Some of these 

 regulators are intended to be used when coal gas is the source of heat, others 

 are constructed for use with paraffin oil, etc., but the former are the 

 most satisfactory, and are the only ones that can be recom- 

 mended. 1 Those that are in most general use are described 

 below. 



A. Electric regulators. Of these Babes' may be mentioned 

 as a type. They are very complicated, uncertain in action, 

 and have no advantage over the following. 



B. Mercury regulators. To explain the principle of the 

 mercury regulators, Chancel's may be described. The gas 

 enters through the glass tube A (fig. 45), which terminates 

 within the regulator in an oblique opening through which 

 the gas issues and passes to the burner through the side tube B. 

 When the regulator is placed within the incubator, the mer- 

 cury contained in the lower part R expands as the temperature 

 rises, so that in time it obliterates the oblique opening of the 

 tube A, and consequently diminishes the volume of gas passing 

 to the burner (in the vertical limb of A there is a small safety 

 opening which permits of a very small supply of gas to 

 the burner, just sufficient to prevent the light going out 

 altogether when the opening below is completely obstructed 

 by the mercury). 



When the temperature within the incubator drops, the level FlG 45._Mercury 

 of the mercury falls and the supply of gas to the burner is regulator, 

 increased. The regulator is controlled by the screw V : when 

 this is turned clockwise the level of the mercury E stands at a higher level for 

 any given temperature, while by turning it contra-clockwise, the volume of 

 mercury in the tube is diminished. This regulator is cheap but not very 

 sensitive, and is only correct within about 3 C. ; an improved form of it 

 has been devised by Arloing. 



C. Ether regulators. Rohrbeck's (fig. 46) may be taken as an example of 

 this form of regulator, the working of which depends upon alterations in the 

 vapour tension of ether at different temperatures. 



1 To ensure as constant a temperature as possible with gas, a pressure-regulator should 

 be affixed to the main, so that the gas always reaches the incubator at a constant 

 pressure. 



