ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
677 
As the temperature rises the air inside the test-tube expands and presses 
the mercury up the small tube until it makes contact with the wire, 
and the current passes. The position of this current regulator in the 
thermostat is seen in fig. 98. 
For the battery, four or five Meidinger elements are sufficient. 
In using the thermostat the flame of the lamp is gradually raised 
until the desired temperature is reached, when the platinum wire of the 
current regulator must be brought just into contact with the mercury. 
According to the author, the variations of temperature do not then ex- 
ceed 0*25° duriDg twelve hours’ work. 
Fig. 100. 
v 
Median longi- I 
tudinal section 
O-z/)- 
Median cross-section. 
Object-Holder of Aluminium for observation of Objects on both 
sides.* Dr. M, Heidenhain describes a new object-holder of aluminium, 
* Zeitschr. f. wiss. Mikr., xiii. (189G) pp. 16G-72. 
1896 
