106 THE MICROSCOPE 



of the hands placed even heavily upon it. The pillar and base 

 are equally heavy and free from any spring. The fine adjustment 

 is exceptionally delicate — one revolution of the milled head moves 

 the body only '1 mm. Each division on the milled head is equal 

 to "OOl mm. The coarse adjustment milled heads are very large, 

 enabling a finer adjustment to be made. The stage is square, 

 measuring 4 J X 4f inches. In the simple model it is flat, with a 

 gap cut out in front, and the standard mechanical stage can be 

 attached to it at will in a similar manner to that of the standard 

 model, being clamped to the limb through an aperture left for 

 the purpose. "When a mechanical stage is supplied at the same 

 time as the microscope, it is fitted with a steady pin entering a 

 second hole in the limb, so that it cannot be attached in an in- 

 correct position. In the best form of instrument, as illustrated 

 on page 105, the square stage has two dovetailed grooves planed 

 in its surface, and the mechanical stage racks up and down 

 these grooves or can be removed at will. This mechanical stage 

 has its actuating milled heads projecting laterally on the right- 

 hand side. The upper one moves the slide laterally and has 

 3 inches (75 mm.) travel, the lower one moves the slide vertically 

 and has a travel of IJ inches (30 mm.). The latter motion is 

 provided with a clamp screw, so that it can be locked to prevent 

 any chance of the slide moving when the instrument is in a 

 horizontal position. This prevents any settling down of the 

 object during photomicrography. Verniers reading to 1/10 mm. 

 are provided to both movements in convenient positions for 

 reading. 



The substage racks up and down on the lower portion of 

 the limb, which is accurately in the optic axis of the microscope, 

 and the mirror fits by means of a sliding fitting on the same slide. 

 The substage has centring adjustments and is of the standard 

 size, but at its upper end is fitted with a dovetailed fitting to 

 receive the condensers or dark- ground illuminators. All the 

 illuminators are mounted on dovetailed slides which slide easily 

 into the dovetailed fitting, and are held accurately in position 

 by a clamping milled head. Each illuminator is accurately 

 centred and of the same length, so that they can be rapidly 

 interchanged while the object is under observation. The front 

 portion of the stage is cut out to enable this to be done, and even 

 an oil-immersion condenser can be changed for a dark-ground 

 illuminator while the slide is under observation. While these 

 illuminators are in use, the tubular portion of the substage is 

 free to receive apparatus which can be used in conjunction with 

 them. The back of the foot of the microscope carries a short 

 vertical post, and when the microscope is placed in a horizontal 

 position for photomicrography this takes the weight of the limb 

 and makes a rigid support under conditions where a slight tremor 

 might ruin the sharpness of a photograph. The body is of the 



