112 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



that the sections of the former were too thick, and that the closed 

 chambers which he described must be open, as they were filled np by 

 the immersion in balsam. Miiller, however, only admits an aperture 

 on the outer side. 



Impressions on collodion do not appear to have given the results 

 expected by the authors who emj)loyed it. On the other hand, the 

 submersion of the valves has equally furnished facts which are 

 wanting in concordance. 



Photographs, again, give only illusory diffraction images, and the 

 suggested examination of the valves by reflected light cannot eliminate 

 these errors. 



To show the difficulty of these investigations it is sufficient to recall 

 the fact that the parts which are much less delicate, such as the con- 

 nective, the raphe, and the nodules, still give rise to very diverse inter- 

 pretations. M. Prinz thinks that these divergences originate in great 

 part from the want of distinctness in the sections obtained by cutting 

 diatoms contained in a medium without consistency, such as gum arabic. 



The author is about to re-examine some diatomiferous rocks with 

 the assistance of Dr. Van Ermengem. 



MICEOSCOPY. 



a. Instruments, Accessories, &c. 



Boecker's Air-pump Microscope. — E. Boecker, of Wetzlar, manu- 

 factures the air-pump Microscope shown in Fig. 7, which enables 



an object to be examined in a 

 ^^^' '^- vacuum under the Microscope, 



and the progressive effects at- 

 tendant upon the exhaustion 

 of the air watched, as well as 

 serving for the more ordinary 

 purposes of an air-pump in 

 mounting. 



The apparatus is secured to 

 the table by the clamp A, and 

 the piston of the pump B is put 

 in operation by the handle C 

 acting on a rack and pinion D E. 

 The chamber F (2| x f in. 

 deei>), in communication with 

 the pump, is pierced with a 

 central aj)erture which is closed 

 by a piece of glass, allowing 

 the light from the mirror G to 

 reach the object placed in the 

 chamber. The latter is made 

 air-tight by a circular glass 

 plate greased at its margin. 

 H is the taj) for readmitting 

 the air. Either a simple or a compound Microscope can be attached 



