438 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
magnification they give if used ns a single lens at the distance of distinct 
vision, or 10 in. This magnification, in addition to focal length and 
numerical aperture, should be engraved upon the mount. He thinks 
that in time the statement of magnification would be recognised as the 
proper description of the lens ; and that the operator would gain greatly 
by knowing exactly the quality of his apparatus. 
White, Jon a — More about Achromatic Condenser Construction. 
[The author advocates use of slides cf medium thickness.] 
Micr. Bulletin (Philadelphia), April 1S99, pp. 9-11. 
Keeley, F. J. — Some further Discussion on Achromatic Condensers. 
[Adjustability of objectives and condensers advocated.] 
Micr. Bulletin (Philadelphia), April 1899, p. II. 
(3) Illuminating 1 and other Apparatus. 
Electrically Heated Stage. — Reichert’s electrically heated stage, 
exhibited at the Meeting of the Society on Mav 17th, is represented in 
figs. 104, 105. 
It consists of a stage and a contact-breaker. The stage is a metal 
case, 24 mm. high, containing a coil which is connected with the main 
circuit m 2 n 2 , and filled with paraffin oil. The regulator consists of a 
contact-thermometer Rr, fig. 104, encased in the stage, and an electro- 
magnetic contact-breaker contained in a separate box. The contact- 
thermometer is connected with the electro-magnet, and closes and opens 
the circuit of the battery B, which goes to the electro-magnetic contact- 
breaker. This latter closes and opens the main circuit. 
When putting the apparatus into action, attention is to be paid to 
the following jioints : — (A) The heating of the stage is effected by the 
main circuit ; (B) The regulation of the temperature is effected by the 
auxiliary current. 
A. Heating of the Stage. — (1) The main circuit is connected with the 
contact-breaker by means of the cable St St', the current thus entering 
the battery. (2) The contact-breaker is connected with the stage by 
means of the cable T T'. The current enters the stage, and heats the 
paraffin oil and thus the whole stage. 
B. Regulation of the Temperature. — The battery is connected at R 
with the contact-thermometer at R\ If now the mercury of the thermo- 
meter is made to rise by the heating of the stage, and thereby touches 
the platinum in this thermometer, the main circuit is interrupted. The 
temperature then begins to fall, the mercury-column again contracts, and 
the main current passes once more through the stage, and the temperature 
begins to rise again, the mercury-column again reaches the platinum, 
and the circuit is once more interrupted. This process is again and again 
repeated. 
The most important point for keeping the stage in action, is to con- 
nect the cables well witli the stage and the contact-breaker. For this 
purpose the parts belonging to each are marked by corresponding letters, 
thus the pin A fits the opening at A ; the pin B fits the opening at B, 
&c. &c. The black cable belongs to the black contact ; the yellow cable 
to the yellow contact. 
Through the coil there passes but a very weak current (0* 2 ampere). 
The contact-thermometer being very sensitive, there is no difficulty in 
