398 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



movemeut. The objective is shown at r. (The author says that it is 

 better to i>roduce the fine adjustment by means of a screw on the 

 end of the tube, similar to the correction adjustment of objectives.) 



To be able to produce a clear image of the sun, the whole of it 

 must be seen, and therefore only low powers can be used. The field 

 must be about 1 mm. in diameter. To protect the eye against the 

 intensity of the light, a number of smoked glasses can be placed on 

 the eye-piece i. 



Two methods were employed by Professor Pringsheim for the 

 temperature determinations * : (a) the insertion of a thermo-electric 

 couple of iron and nickel into the drop, the results being read off by a 

 galvanometer ; and (h) the introduction of small crystals of substances 

 of known melting-point. For the latter purpose two substances, azoxy- 

 benzol, which melts at 45° C, and mint-camphor, with its melting- 

 point 35- C, were found most convenient. 



Waechter's (or Engell's) Class or Demonstrating Microscope. 

 — This instrument might readily be mistaken for an ordinary brass 

 candlestick. Its original form is figured by Harting j ; Figs. 63 and 



64 show it as im- 

 F^«- '^^^ ^'''- «*• proved by Waechter, 



the lower part being 

 seen in Fig. 63 in 

 section. 



The body-tube, 

 carrying eye - jjiece 

 and objective, slides 

 in an outer " sprung " 

 tube which is at- 

 tached at its lower 

 end to a conical base. 



which forms a wide support for the instru- 

 ment to stand ujon when not in actual 

 use. The inside of the base is polished 

 so as to reflect light upon opaque objects. 

 The ends of the slides are held beneath a 

 metal ring at the lower end of the base, as 

 shown in Fig. 64, and they can be removed 

 by turning them round till they coincide 

 with the two openings in the ring. The in- 

 strument is held up to the light and focussed 

 by sliding the inner tube in the usual way. 

 It can be secured at any given focus if desired by the milled clamp 

 ring near the top of the sprung tube. A cover fits over the base 

 (shown in Fig. 63) and is pierced with a small hole to act as a dia- 

 phragm with high powers. 



The instrument is intended for class demonstration. 



* See translation of Prof. Pringshtim's Researclies by Prof. Bavley Balfour, 

 Quart. Journ. Micr. Sci., xxii. (1882) pp. 7(;-ll2 (2 pis.). 



t Harting, P., ' Das Mikroskop,' iii. (1866) pp. 196-7 (2 figs.). 



