810 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



to fit agaiast the pillar h of the Microscope. The piece g g' turns on g', in 

 order that the stage may be slipped on the Microscope, and this done, it is 

 held in position by means of the steel-pointed screw i. The piece c c' is 

 terminated at each end by a milled head, which, in connection with the 



Fig. 220. 



rackwork on d d', moves the stage backwards and forwards. These two bars 

 d d' are also connected with a a', upon which the slide rests. Lateral move- 

 ment is obtained through e e, which is a slotted cylinder terminated at each 

 end by the milled heads h h'. 



The scales /and/' enable any particular point of the preparation to be 

 found again, but if the slide has been removed from the stage it is 

 necessary also to note the reading of the scale /". 



Borden's Electrical Constant-temperature Apparatus.* — Dr. W. C. 



Borden describes an apparatus for maintaining a constant temperature, 

 which will not easily get out of order, and can be depended upon to maintain 

 the temperature desired, intended more especially for the use of those who 

 have no gas at command, but have to use either petroleum or alcohol as a 

 source of heat. It can be left for hours with the certainty that when again 

 examined the heat will not have gone above a certain point or have dropped 

 at any time more than one-half or possibly one degree below it. 



The general form of the entire apparatus is shown in fig. 222, and the 

 regulating thermometer in fig. 221. The battery used is the ordinary 

 gravity battery used in telegraphy which gives a current of nearly constant 

 quantity, and requires but little attention. 



The regulating thermometer (fig. 221) is made by taking a small glass 

 vial, filling the lower part with mercury and the upper with 95 per cent, 

 alcohol, corking it tightly and passing a small glass tube through the 

 cork at the bottom. The cork must fit very closely and should be made 

 impervious to water by soaking in melted paraffin for several hours. The 

 top of the tube is to be loosely corked and two wires passed down into it 

 through the cork without touching each other — one A well down into the 

 mercury, and the other B free above it. This regulating thermometer is 

 now hung in the water-bath supported by the cork C, and when the 

 temperature of the bath, as shown by a standard thermometer, has reached 



» Amer. Mou. Micr. Journ., viii. (1887) pp. 131-3 (2 figs.). 



