COLLINS'S STUDENT'S STAND. 105 



in point of finish, is equal to the students' micro, 

 scopes of first-class manufacturers. The semicircular 

 form given to the arm carrying the body increases the 

 strength and solidity of the instrument, although it is 

 doubtful whether it adds to its steadiness when placed 

 in the horizontal position. The straight body rests 

 for a great part of its length upon a parallel bar of 

 solid brass, ploughed into which is a groove for the 

 reception of the rack attached to the body, the groove 

 being of such a form that the rack is held firmly while 

 the pinion glides smoothly through it. A steady uni- 

 form motion is thus obtained, and which almost renders 

 the fine-adjustment unnecessary. The fine-adjust- 

 ment screw is removed from the usual position and 

 placed in front of the body, just above and in front of 

 the Wenham prism. The binocular bodies are inclined 

 at a smaller angle to one another than in most instru- 

 ments ; nevertheless, the range of motion given to the 

 eye-pieces by the rack and pinion, enables those whose 

 eyes are widely separated to use the instrument with 

 comfort. The prism is so well set that it illuminates 

 both fields with equal intensity. The stage is provided 

 with rectangular traversing movements to the extent 

 of an inch and a quarter in each direction. The milled- 

 heads which effect these are placed on the same axis, 

 instead of side by side, one of them the vertical one 

 being repeated on the left of the stage, so that the 

 movements may be communicated either by the right 

 hand alone or by both hands acting in concert. The 

 stage-plate has the ordinary vertical and rotatory motions, 

 but to a much greater extent than usual ; and the plat- 

 form which carries the object is provided with a spring 

 clip to secure the object when the stage is placed in 

 the vertical position. A regularly fitted sub-stage with 

 centring screws is made in the usual way to carry an 

 achromatic condenser, diaphragm, polarising and other 

 apparatus. 



Collins's Student's Microscope (fig. 59) has a 10-inch 

 body and a draw- tube for increasing its length. The 

 diameter of the tube is of full English size ; the field 

 is consequently large. The fittings for objectives and 



