50 SELECTION AND USE 



The Jackson Model. The special characteristic of this 

 model lies in the fact that the ' ' ways " of both the coarse and 

 fine movements are brought as close as possible to the optic axis 

 of the instrument. In the Ross model the coarse movement is at 

 a considerable distance from this axis, and any lateral motion 

 which may take place on the sliding part is greatly magnified 

 at the axis of the body the tram verse bar, which supports the 

 latter, acting like the long arm jf a lever to greatly multiply 

 that which at first was very insignificant. Hence the advan- 

 tages which the Jackson model presents are great steadiness and 

 the fact that, in common with the Boss model, it affords abun- 

 dant room underneath the stage for those accessory methods of 

 illumination which are indispensable in the highest class of 

 work. It is almost impossible to attach to the smaller patterns 

 of the Continental model a convenient sub-stage, carrying 

 polarizer, achromatic condenser, paraboloid, etc., while the 

 model under consideration is specially designed to receive 

 these important accessories. 



This model is a very general favorite both with English 

 and American makers. Amongst the latter it has been adopted 

 as the best for all first-class stands. The engraving, Plate II, 

 shows a very excellent form of this model by the Bansch & 

 Lomb Optical Company, and known as their Large Student 

 Stand. It will be observed that the body of the microscope is 

 supported along its whole length by means of a tube attached to 

 the arm, which is hung between two pillars, so as to give great 

 steadiness. To add to this steadiness, all sharp angles are 

 avoided, and the arm is gracefully curved instead of joining the 

 body at a right angle, as in the Ross model, and all of those 

 made strictly after the so-called Continental pattern. 



Tlie Continental Form. Most of the stands made by 

 the better class of French, German, and Austrian microscope 

 makers are characterized by a low, compact form, and great 

 solidity and simplicity of construction. They are intended to 

 be used chiefly in a vertical position, and hence the bodies 

 are short, and the space beneath the stage is contracted to the 

 last degree. And as a low price is an important feature in these 

 microscopes, the coarse movement is generally secured by 



