312 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



introducing hot or cold water and the tube b for carrying it away. The 

 former is attached to a T tube — one branch a being connected with a 

 vessel of hot water, and the other a" with cold water, a pinchcock closing 

 the one not in use. A double T tube is in connection with b, through 

 one branch of which the water ordinarily flows in drops controlled by the 

 screw c. The object of the double tube is to facilitate an almost in- 

 stantaneous change of temperature. If the pinchcook d on the second 

 branch is opened at the same time as the cold-water vessel is placed in 

 connection with the stage the water will rapidly circulate, and the stage 

 will be filled with cold water only, so that in a few seconds the temperature 

 may be lowered 30°. 



Dr. Flesch at the time his paper was written was not wholly satisfied 

 with his apparatus, and expected to improve it. 



Loivit's Hot Stage for High Potvers* — The thickness of the ordinary 

 hot stage does not allow the condenser to be brought close to the under 

 side of the slide, so that the object is not in the focus of the illuminating 

 beam, and the use of high powers is obstructed. Dr. Lowit's hot stage 

 (fig. 73) is intended to remedy this difficulty. 



Fig. 73. 



Fig. 74. 



In general form the stage is like that of Strieker but thinner ; the 

 water circulates by means of the two tubes B B' and the internal tubing 

 shown by dotted lines. The screws A A' are for centering. 



Into the central opening C can be introduced the upper of the two 

 lenses of a condenser, the upper lens, as shown in fig. 74, being much coned 

 away, so that the top surface lies flush with the 

 stage. The object can thus be placed in the focus 

 of illumination, and the full effect obtained even 

 with homogeneous-immersion lenses. 



To maintain a constant temperature the author 

 finds it better to admit the water from a vessel in 

 which it is kept at boiling-point, and as soon as 

 the temperature in the stage has risen to 30°-40° C. 

 to check the flow by closing the outflow tube until the water can only 

 issue in drops ; by regulating the outflow the chamber can be maintained 

 at any desired temperature. With a slow circulation, however, the thermo- 

 meter will not indicate the temperature of the object, but only that of the 

 water in the neighbourhood of the bulb, which will differ according to the 

 side at which the water enters, the water of course being colder towards 

 the exit side. Thus the thermometer might register 50° C. when the hot 

 water enters at B' and 40° C wlien it is admitted at B, so that in the 



* Zeitschr f. Wiss. Mikr., ii. (1885) pp. 43-6 (1 fig.). 



