240 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



The adjustment is controlled by the position of the fulcrum, and in 

 the DDH the parts of the lever bear the relation of 2 to 1. The slide 

 is very near the optical axis, the weight of the body-tube and optical 

 parts only being moved, regardless of the length of the arm. This 

 permits the use of larger stages without detriment to the fine-adjust- 

 ment. With it, no force greater than the weight of the body-tube and 

 its accessories is exerted on the cover-glass, for at the moment of contact 

 the further movement of the screw has no action whatever upon the 

 adjustment, and in this way damage is prevented. 



Hensoldt's New Micrometer Microscopes.* — Fig. 43, numbered 

 48 in the makers' catalogue, illustrates an instrument intended for 



reading off meridian circles and geodetic in- 

 strumeuts. The objective is achromatic, the 

 flint lens being turned towards the gradu- 

 ation. The ocular is achromatic and or- 

 thoscopic. In order to give a maximum 

 light-intensity the objectives are constructed 

 of as diminished a focal length as possible ; 

 they thus require a weaker, and therefore less 

 tiring, eye-piece. The micrometer-box is dust- 

 proof, and the movement is destitute of dead- 

 way. The measuring apparatus is double- 

 threaded, and there are 5-10 teeth in the 

 field of view, the drum being divided into 

 60, 100, or 120 parts. The illuminator is 

 rotatory, to give maximum light, and the 

 micrometer-screw has a movement of 0*25 

 to 0*3, or * 5 mm . 



Application of Microscopes as a Means 

 of Demonstration in Public Museums.f — 

 G. Marktanner-Turneretscher, while fully 

 cognisant of the difficulties arising from ma- 

 nipulation and expense which would attend 

 the introduction of Microscopes into public 

 museums, yet thinks that the interest which 

 by the observation of Microscopic objects deserves 

 He, therefore, discusses with considerable detail the 

 principles which should underlie the construction of a museum Micro- 

 scope. The instrument should be inclosed within a suitable glass case, 

 in such a manner that the ocular protrudes. The object-stage should 

 be rotatory and should carry at least twelve preparations : the rotatory 

 apparatus should be controllable from the outside. The adjustment, 

 as strong magnifications would never be required, should not be by 

 micrometer-screw, but by sleeve-work with rack-and-pinion ; he re- 

 commends a lever action in preference to milled-heads. There should 



* Hensoldt and Sons, Wetzlar, Catalogue, Astrononiische-Optik, pp. 7, 8. 

 t Museumskunde, v. pp. 39-42. 



Fig. 43. 



would be aroused 

 to be encouraged. 



