ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



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done by a set-screw Jc, on the one side, and a spring I on the other. On 

 the under side the carriers j form bars m, of the breadth of the ring g, 

 to which they are closely applied while, sideways, they somewhat pro- 

 ject beyond the partitions h, so that no dust can penetrate into the 

 objectives between these walls and the carriers. 



In use, the ring g is pushed round until the desired objective is 

 under the tube d. When this occurs, a spring automatically snaps and 

 holds the objective rigidly in its place. Any adjustment required is 

 easily done by the set-screws Jc, Jc. The rotation of g is to be done by 

 means of the little handles q, in order to avoid any possible disturbance 

 of the centring of the objectives. To prevent entrance of dust during 

 an exchange of oculars, the ring g is rotated so that one of the inter- 

 shaft spaces comes under the tube d. 



Microscopist's Electrical Lamp. * — Fig. 46 represents this lamp 

 about half size, as devised by T. Tammes. The light source is an 



Fig. 46. 



almost spherical electric incandescent lamp of about 4 cm. diameter. 

 It is made of 5 or 10 candle-power, the first sufficing for ordinary pur- 

 poses. The carbon filament is wound several more times than is usual, 

 and when in use the planes of the coils should be perpendicular to the 

 observer. In the figure the thread is not visible as the glass is ground. 

 The frame is of cast iron, and of such a height as to just fit between 

 the foot and stage of an ordinary Microscope. The lamp can thus be 

 brought close to the mirror. The sides so enclose it that an operator 

 is confined to his own lamp, and not affected by. that of an adjoining 

 observer. The open back reduces inconvenience from excess of heat. 

 The open front permits of the insertion from above of coloured screens. 



* Zeitschr. f. wiss. Mikr., xviii. (1902) pp. 280-5 (1 fig.). 



