672 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Martens' Ball-jointed Microscope.*— This (Fig. 118) is the 



invention (patented) of A. Martens, of Berlin, and is thus described :— 



In the observation of metals in their microscopical relations it 



is desirable to be able to give the Microscope the greatest possible 



power of movement, since the 

 Fig. 118. objects for the most part do 



not admit of small fragments 

 being taken from them. A 

 Microscope was originally made 

 for the author by Zeiss, in 

 which movability of the stand 

 was obtained by three hinge- 

 joints, which could be clamped 

 up by a screw so that the tube 

 remained quite firm at every 

 angle ; indeed it was firm 

 enough to admit of a fine ad- 

 justment being used. It was, 

 however, too limited in its 

 action, it worked properly only 

 in a line perpendicular to the 

 object, and in order to examine 

 i|"Y^B^H»Jpli^ the neighbouring parts either 



fr— ■ — ^^HJSP ^^^ tII * ne heavy object or the equally 



m §1 heavy instrument had to be 



- M ■■ moved. 



In the new construction 

 the inventor has obtained far greater movability. Instead of the 

 hinges, ball-joints of large diameter are made use of, the balls being 

 hollow and clamped between two annular plates, placed unsym- 

 metrically with regard to the centre of the ball. The plates are 

 forced together by the action of a screw, a strong spring between 

 them separating them again when the pressure of the screw is 

 slackened. Thus a clamp, firm but readily loosened, is obtained. 

 One or more ball-joints can be used for each stand. 



Polarizing Microscopes.! — Prof. J. B. Listing objects to the 

 term " polarizing Microscope," so commonly applied to the Norrem- 

 berg (or Hofmann) polarizing apparatus. The use of the name 

 " Microscope " is not only incorrect in itself but it conflicts with that 

 which properly belongs to a Microscope by means of which small 

 objects are examined by polarized light, such as sections of minerals, 

 crystals, hairs, muscle-fibres, &c. The objective of the true polarizing 

 Microscope retains its ordinary dioptrical function, but in the other 

 case no question of amplification comes into consideration (but rather 

 a large angular diminution), the instrument without the lower collect- 

 ing-lens being in reality an inverted astronomical telescope with the 

 eye-piece turned to the object. 



* Zeitschr. f. Instrumentenk., ii. (1882) p. 112 (1 fig.). 



+ Bericht wiss. Apparate Loud. Internat. Ausstellung im Jahre 1876 (A. W. 

 Hofmann, 1878-81) pp. 367-8. 



