310 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



vertical column on which the escape tube is supported. This column is 

 firmly fixed in the stage of the Microscope, its axial screw terminating 

 above in a milled head h. h and i are tubes for gas.* 



Dr. Klein saysf that in the employment of this apparatus several 

 difficulties are encountered. For instance, the temperature of the water 

 receptacle is only in part controlled by the regulator, and the tem- 

 perature of the stage is subject to variation according to the rate at which 

 the water flows into and escapes from it, so that unless great care is 

 taken in the adjustment constancy cannot be relied on. Another practical 

 difficulty lies in the fact that the temperature of the w^ater in the 

 receptacle is different from that in the stage, the rate of flow being so 

 inconsiderable that there is necessarily a great loss of heat by radiation 

 from the metal surface. If the stage is not fitted with a thermometer 

 this difierence of temperature may be determined once for all by com- 

 parative measurements, so that the true temperature of the stage can 

 then be known at any time by deducting the ascertained loss of heat, 

 i. e. the ascertained difierence above referred to, from the temperature to 

 which the regulator is adjusted. 



Fio. 70 



Prof. Banvier | has modified the preceding apparatus as shown in figs. 

 70 and 71. In the centre of the stage A (fig. 70) is a horizontal slit/, in 



* In the apparatus described in the Quart. Journ. Micr. Sci. the water was in tlie 

 first instance conveyed to a loop-shai)td metal tube surrounding the upper part of the 

 objective for the purpose of keeping it warm, a vulcanite ring preventing the heating 

 of the Microscope-tube. From tlie loop the water passed to the stage. 



t Burdon-Sanderson, op. cit., p. 7. 



X Ranvier, L., ' Traite technique d'Hifltologic,' 1875, pp. 41-2 (1 fig.) 



