ZOOLOGY AND BOTANY, M<JROSCOPY, ETC. 



Ill 



construction of which a new principle for regulating the temperature has 

 been applied. The general design is shown in fig. 7. 



A is a metal box, with inlet and outlet tubes a and d. A regulating 

 valve is attached to a, and at b and c are openings, provided with screw- 

 caps. The water in the flask B is heated up to 60°-70° C, and, after 

 flowing through the hot stage, escapes at G. The means of regulating 

 the temperature are shown in fig. 8. The water passes from a through 



the closed cylinder I, which projects into air-chamber g. The volume of 

 air in g varies with the temperature of the water, while the pressure of 

 air in g and I is kept constant by the piston k, which slides freely in the 

 tube m. Hence the temperature of the water corresponds to some position 

 of the piston h. This carries at one end a flat plate p, by which the exit 

 tube d is closed. The exit tube d not only slides through i, but can be 

 adjusted by means of a screw-collar on i. To set the apparatus, water of 

 a higher temperature than that required is allowed to flow through, and 



