238 SUMMARY OF CURRENT RESEARCHES RELATING TO 



MICROSCOPY. 



A. Instruments, Accessories, &c* 

 (1) Stands. 



Ladd's Student's Microscope. — This instrument (fig. 34), kindly 

 presented to the Society's Collection by Mr. Wynne E. Baxter, was 

 exhibited at the Meeting on May 18, 1004. It was made about 1864. 

 Its features are : a very light tripod foot, consisting of a framework of 

 tubes ; a body fixed on a frame, which slides on a straight dove-tailed 

 bar, on the Jackson plan ; the substage slides on the same bar, and is 

 movable by rack-and-pinion, whilst the stage, which is also fitted in 

 the same dove-tailed groove, is fixed. 



Motion is not imparted to the body by rack-work, but by a chain 

 working round a spindle turned by the milled head, which gives a 

 movement of remarkable smoothness and free from backlash. A 

 part of the chain is visible in the figure, above the top of the dove-tailed 

 bar. 



The fine-adjustment is made by a lever which hangs down from a 

 collar formed on the right-hand milled head of the coarse-adjustment. 



The mechanical stage is also moved by chains in both directions. 



The substage referred to is peculiar, and consists of two movable 

 plates carried by a third plate which is fixed to a bracket that slides in 

 the dove-tailed groove already mentioned. 



The centring of the substage is effected by means of the two movable 

 plates. The upper plate is pivoted on the lower, and the latter is 

 pivoted on the fixed plate. The pivot of the upper plate is seen in the 

 figure, to the right of the tube for receiving the condenser. The pivot 

 of the lower plate is to the front of the tube, and is hidden by the upper 

 plate. Motion is given to each plate by means of a pinion geared into 

 a short rack cut in the edge of the plate near the corner. The pinion 

 and milled head for moving the lower plate are seen in the figure, and 

 the pinion for moving the upper plate is in a corresponding position on 

 the other side. Owing to the positions of the pivots, the movements 

 of the plates are at right angles to one another, so that the condenser 

 can be adjusted to the axis of the instrument. 



The mechanical stage is moved in both directions by chains passing 

 round spindles. 



There are two eye-pieces and two object-glasses, of 1 in. and £ in. 

 focus. 



This Microscope is described in Carpenter, 4th edition, 1864. 



* This subdivision contains (1) Stands; (2) Eye-pieces and Objectives; (3) Illu- 

 minating and other Apparatus; (4) Photomicrography; (5) Microscopical Optics 

 and Manipulation ; (0) Miscellaneous. 



