428 SUMMARY OF CURRENT RESEARCHES RELATING TO 



vessel / containing the fluid under examination, and the other com- 

 municates with a glass tube h leading into a bottle. There is a second 

 tube i with an indiarubber ball k, having an orifice m at its upper end. 

 The glass plate is laid on the stage of the Microscope, and the opening 

 in the ball closed with the forefinger ; the ball being first pressed 

 between the middle finger and thumb of the left hand, and then re- 

 laxed, the fluid will be di'awn from the vessel / into the bottle. 



When the taps are completely open, the fluid flous so quickly that 

 the particles which it contains are not seen, but by more or less closing 

 one of the taps, they either pass slowly across the field, or (by quickly 

 shutting them in the field) they can be retained for closer inspection. 

 Pressui-e on the indiarubber ball will also cleanse the apparatus with 

 water after using it. The channel is from 0*2 mm. to 1 mm. in 

 depth. 



The designer adds that the " apparatus is also suitable for 

 drawing-room use, when say a binocular Microscope is exhibited for 

 the amusement of spectators. The apparatus can be easily adjusted 

 so as to pass a whole microscopic aquarium over the field of view." 

 It can also be connected with a hand Microscope constructed for it, 

 which when used is held towards the light, and in this way is useful 

 on excursions. The vessel which holds the fluid must, however, be 

 provided with a fine sieve, the meshes of which must correspond with 

 the size of the channel. The material — mud, sand, chalk, clay, &c. — 

 is rubbed over the sieve, and a little water poured on so that the finer 

 parts may be washed through. It can also be used as a moist chamber, 

 in order to observe the development of the various infusoria, diato- 

 maceae, bacteria, &c. 



Moist Chamber.* — Mr. R. Hitchcock finds the following very 

 convenient for cultivations : — 



A piece of glass, 4 in. square, is placed upon a support so 

 that it is about on a level with the top of a dish to hold water — an 

 ice-cream saucer is what he used. A piece of blotting-paper is then 

 placed on the glass, and the edge allowed to dip into the water. 

 Objects to be examined are placed on large cover-glasses, and either 

 covered with a small cover, or left exposed. These cover-glasses are 

 laid upon the blotting-paper and covered with watch-glasses. A 

 single large watch-glass of 3^ in. diameter may be used, or a number 

 of small ones, one for each specimen. Objects can be kept fresh and 

 moist in this way, with far less trouble than by any other method he 

 has tried. 



Hartnack and Prazmowski's Polarizing Prism.f — It is sur- 

 prising that this prism is not to be found in England, when it 

 presents such advantages over the old form of Nicol prism. As this 

 may be due to the fact that the description of it has not hitherto 

 appeared in English, we subjoin a translation of the original article 

 by its designers : — 



" The Nicol prism possesses valuable qualities which unquestion- 



* Amer. Mon. Micr. Journ., iv. (1883) pp. 56-7. 



t Aiinales de Chiinie et de Physique, vii. (1866) pp. 181-9. 



