THE REGULATION OF TEMPERATURE. 57 



made as small as is consistent with safety. If the temperature to be 

 maintained in the bath is very near to or below that of the hydrant 

 water, the latter, before entering the circulating system, is passed 

 through coils of metallic pipes which are surrounded by ice. If the 

 desired temperature is not much above that of the atmosphere, the 

 cooling effect of the surrounding air upon the exterior of the bath may 

 suffice, in which case the circulation of hydrant water is discontinued. 

 Finally, if the temperature to be maintained is considerably above that 

 of the atmosphere, the system within is connected with one on the out- 

 side, thus forming a closed circulating system which is partly within 

 and partly without the bath, and through this hot water is circulated by 

 means of a pump. The pump may be situated anywhere in the system, 

 i. e., either within or without the bath. At some point outside, provision 

 is made for heating the water by gas as it passes through the sj^stem. 



Thus far, provision for the cooling surface only has been made. Not- 

 withstanding the application of heat, and sometimes a good deal of it, 

 the circulating system mentioned above is, essentially, a cooling device, 

 inasmuch as its purpose is to reduce the temperature of the bath below 

 that which is to be maintained. In this system, for economical reasons, 

 gas is used for heating rather than electricity, but care is taken so to 

 regulate its flow that a "cooling margin" will be maintained, whatever 

 may be the fluctuations in the pressure upon the gas. Since the "cool- 

 ing surface" is not subject to exact regulation, it must never be allowed 

 to become, in effect, a "heating surface, ' ' for in that case the thermostat 

 becomes useless. 



The "heating surface" usually consists of one or more copper cyl- 

 inders, in which are inclosed ordinary electric lamps, which serve as 

 stoves, whose purpose is to overcome the "cooling margin" If that 

 margin is small — and it should be made as small as possible — the con- 

 sumption of electricity is not large. Lamps are used rather than other 

 forms of electric heating devices, because one can always select among 

 them stoves whose capacity is suited to the work to be done, and 

 because they heat up and cool down quickly, which is an important 

 element in temperature regulation. 



The circulation of water over the cooling and heating surfaces is 

 effected by means of pumps, and it will be seen later that a single 

 pump may be made to circulate the water over these and also through 

 the cooling system. The air in the baths is circulated by means of 

 rotating fans. 



THE SCHEME FOR ELECTRICAL REGULATION. 



The device by means of which the margin of under-temperature pro- 

 duced by the so-called "cooling surface" is exactly and automatically 

 overcome is shown in Figure 29. Everything not essential to an under- 

 standing of its plan is omitted. It consists, in its simplest form, of (1) 



