APPARATUS FOR MAINTAINING CONSTANT TEMPERATURE. 



3<yb 



an overflow tube to a waste pipe. Moreover, since the tem- 

 perature of tlie stage is regulated by the rate at which the 

 heated water is allowed to flow through it, and this again is 

 made to depend upon the difference of level between the 

 orifice of the exit tube which leads from the stage aud the 

 height of the boiling water in the reservoir, and since this 

 requires a rather complicated screw mechanism accurately to 

 adjust the level for diflPerent temperatures (not to mention 

 the numerous india-rubber tubes requisite for connecting the 

 various parts of the apparatus), it is evident that, although 

 the apparatus in question may be well enough adapted for a 

 laboratory, it is less applicable to individual and private 

 work. The apparatus to be here described, the main prin- 

 ciples of which are a constant circulation of water and the 

 introduction of a gas regulator, will, it is believed, be found 

 simple and convenient in application, and capable of main- 

 taining with almost absolute constancy any desired tempera- 

 ture for an indefinite time. 



The apparatus consists of a closed brass box, oblong in 



Fig. 1. 



^i feiiltiMiiiltllli iliilii 



Fig. 1. — a. View of warm stage with inlet and outlet tubes, unconnected 

 with heating apparatus, c. Horizontal section of stage, showing the manner 

 in which the thermometer is passed into tiie central chamber, and the direc- 

 tion of the current of water in the stage. 



form (fig. 1, a), which rests upon the stage of the microscope, 

 a cylindrical chamber (fig. 2, b, in vertical section) being left 

 in the centre of the box for the transmission of light from 

 the mirror to the object (as in Strieker's warm stage). From 

 each end of the box a tube passes (inlet and outlet) , and the 

 tubes are connected the one to the other by india-rubber 

 tubing, so that there is thus formed a closed circuit, which, 

 when the apparatus is ready for working, is entirely filled 

 with water. A vertical reservoir (fig, 2, c), of not much 

 greater capacity than an equal length of the connecting tube, 

 is interpolated in the circuit at a point not far from the inlet 

 of the stage, in such a manner that the upper end of the 

 reservoir is connected with the inlet tube, the lower end 

 with the outlet. The reservoir surrounds the bulb of a 

 mercurial gas regulator (fig. 2, d; and fig. 3), and is heated 

 below by a minute gas flame ; it will be readily understood 

 that the heated water in the reservoir must rise up through 



