268 



SUMMARY OF CURRENT RESEAROBGES RELATING TO 



fully adjusted and focussed, a taper is lit, and the eye remains at the 

 eye-piece until the critical point is reached. The glass tube t, with 

 its point terminating just below the edge of the slide, is connected 

 with the mouth during the experiment by a small rubber tube. As 

 the temperature slowly rises, a constant current of small bubbles of 

 the warm breath (whose temperature, 32'', only assists the operation) 

 may be blown with little fatigue through the tube, to effect a thorough 

 intermixture of unequally heated layers in the water stratum. The 

 determination of the temperature of disappearance of the bubble is 

 easily obtained within five minutes, and that of its reappearance in 

 about the same time, A low-power objective may be carefully wiped 

 if its anterior lens is dimmed by flying drops or rising vapour, when a 

 high temperature is being attained ; but it is best to insert the whole 

 objective in a small, narrow glass beaker floating upon the surface of 

 the bath over the preparation. 



The aj)paratus, as thus constructed, may, the author thinks, be 

 found the most convenient warm stage when high temperatures are 

 required ; but another still more simple, lately devised, will best serve 

 for the determination of carbon dioxide, and consists of the following 

 parts : — 



First, a shallow glass tank (Fig. 52), with thin and well-annealed 

 sides, of size sufficient to enclose the slide, upon which the thin 



section is mounted. For this purpose I use a small chemical beaker 

 B, with the thinnest bottom, and with its upper portion cut off, forming 

 a thin round glass tank, about 6 cm. in diameter, and 3 cm. deep. 



Secondly, a plate of copper or brass, like that used in Schultze's 

 apparatus, or more simply one of the form represented in the figure d e. 

 Its dimensions, proportioned to those of the beaker-tank and of the 

 stage of a large Microscope, are as follows : — Length, 23 cm. ; 

 diameter at centre, 6 • 5 cm. ; width of arms, 3 • 5 cm. ; central aperture, 

 2 • 5 cm. ; height of wire support, 13 cm. ; thickness of plate, 1 mm. 

 Each arm is wrapped in pasteboard, to prevent radiation, to the extent 

 indicated by the shaded portion. 



Thirdly, a delicate thermometer, with a small, short bulb bent at 

 right angles to the stem, and a very fine column, to obtain sufficient 

 sensitiveness to minute variations of temperature, and complete 

 immersion of the bulb in the small volume of liquid employed in the 

 bath. The scale need not exceed in range from about 20° to 32° C, 

 the thermometer being of such length that when in position the scale 

 from 27° to 30° C. may be on the level of the eye-piece of the Micro- 



