24 PRACTICAL MICROSCOPY. 



is 3J inches from the table. The body is 5 inches 

 long and the draw-tube also 5 inches in length, marked 

 with a ring to show the standard length. The diameter 

 of the body-tube is 1*4 inch. The stage has a revolving 

 concentric movement, the mirror and substage can be 

 made to swing over the tube, and there are spring stops 

 to indicate when they are in a line with the axis of the 

 instrument. The lower end of the main tube is fitted with 

 the Butterfield broad-gauge screw, forming an adapter 

 which carries the Society thread. The price of this instru- 

 ment in walnut case is, with one eye-piece $40, equal to 

 about SI. Ss. of our money, or with j-inch and |-inch 

 objectives I2/. It is shown by Fig. 14. 



After the introduction of these swinging substages by 

 Zentmayer the manufacture of them was taken up in this 

 country by Messrs. Ross and Co., of New Bond Street, so 

 that those who desire to be furnished with the latest im- 

 provements or modifications of the instrument can easily 

 be supplied. The methods of construction are very similar 

 both in the American and English instruments, though the 

 superior workmanship of details in Fig. 15, over the 

 Biological stand of Bulloch, is only to be expected owing to 

 the difference in price. 



This instrument is constructed on the Jackson model, 

 and is particularly free from tremor. The coarse adjust- 

 ment is effected by means of the ordinary rack and pinion, 

 the fine movement being worked by the action of a micro- 

 meter screw acting on a lever, by means of which the body 

 is not touched when using the fine adjustment, and as the 

 length is not changed, the relative distance of object-glass, 

 binocular prism, and eye-piece remains the same. 



The substage bar which carries the mirror, condenser, 

 and other substage illuminating apparatus, swings from a 

 pivot placed behind the stage, the axis passing through the 



