278 NEW TRAVERSING STAGE 



easily moved by the lever either in the same or in parallel planes, but 

 at right angles to each other ; while if both be moved at the same 

 time, a diagonal motion is obtained at the pleasure of the operator. 



This plan of a traversing stage has many advantages, it is in the 

 first place simple in its construction, and is very easily managed — 

 and as the end of the lever to which the hand is applied moves in all 

 cases in exactly the opposite direction to that in which the stage is 

 moved by it ; and as the compound microscope always inverts the 

 image of the object under examination, the object will appear to move 

 in the direction of the hand. But the great objections to this form 

 of the traversing stage, are that the lever is very much in the way, 

 and being attached to one of the extreme angles of the stage, when, 

 it is in use, the strain is thrown more upon those parts of the stage 

 in the vicinity of the lever, which wear away more rapidly than the 

 others, and soon impair the correct working of the instrument. 



The next mode of producing a traversing motion, is that usually 

 known as Turrell's plan, and is described by that gentleman in the 

 49th volume of the transactions of the Society of Arts. In this 

 mode the lever is entirely dispensed with, and the different motions 

 are communicated to the stage plate, by two milled heads placed 

 together, at the right hand side of the stage, and turning upon con- 

 centric axes. The motion of one of the plates of the stage is pro- 

 duced by turning one of the milled heads attracted to a pinion which 

 works in a rack attached to the under side of the plate. The motion 

 of the other plate is produced by the other milled head which works 

 a screw, in a thread attached to the under side of the second plate ; 

 and by working the two milled heads at the same time, a diagonal 

 motion is given to the stage. But apart from the complexity of 

 this arrangement and its great liability to get out of order, it has 

 several very serious defects, the greatest one being that in order to 

 produce a diagonal motion in some directions it is necessary to use 

 both hands, an objection which this form of stage was expressly 

 designed to meet, but which it only partially removes. 



In the microscope which I have now the honor to bring under the 

 notice of the Canadian Institute, this difficulty is entirely overcome, 

 and by a combination of the lever and the screw, the advantages, 

 without the defects, of both Mr. White's and Mr. Turrell's plans are 

 secured. 



I have placed immediately under, and running the whole way 

 across the stage, the lever / g Fig. 1. on which for about two inches 



