Suggestions regarding the Mechanical Design of Microscojjes. 139 



liearings should be planed on one block of metal on one machine 

 to ensure their being parallel and remaining so. This is only 

 done on a few instruments at present. The petrological instru- 

 ment might well be modified along these lines, the body tube with 

 its many doors and slots being abolished altogether. Nose-piece, 

 eye-piece, and all intermediate apparatus being attached to a bnr 

 carried by the adjustments, the eye-piece to be carried on a rack- 

 work extension. To exclude light a simple bellows could be 

 sprung on at top and bottom of this " tube." Many instruments, 

 including some of the most complete, appear to be designed with a 

 view to compactness when in their cases. This is no doubt a 

 desmable feature, but nothing should be sacrificed to attain it. 

 The commonest fault is the position of the focusing slides. With 

 many instruments the body is one or two inches out of its slides 

 when a short focus objective is in use with a nose-piece or changers 

 (one or the other appliance is in universal use). There is no 

 possible reason for this fault except the striving after compactness 

 — and this particular fault is the commonest cause of lack of 

 rigidity in the modern microscope. 



The same tendency one must suppose is the. explanation of the 

 inadequate foot still commonly fitted, and the lack of room under 

 the stage for substage and mirror manipulation. 



All this is perhaps excusable in student's microscopes, which 

 sometimes have to be carried about, but is quite inexplicable in 

 instruments designed for the advanced worker or the laboratory, 

 such being rarely moved from the room in which they are used 

 from one year's end to another. The type of foot which combines 

 the maximum of rigidity and convenience is one in which the limb 

 is swung between two strong vertical pillars which are cast in one 

 piece with a wide-spreading flat triangular base, the apex of the 

 triangle being toivards the front, as in a " flat-iron " ; this triangle 

 to rest on cork pads at the angles. Levelling screws may be added 

 at the corners for use in micro-photography. 



For laboratory work I would make this flat triangular base so 

 large that a glass bell-jar placed over the instrument would rest 

 on the base, its circumference in no place projecting over the sides. 

 The trunnions should be placed at or above the level of the surface 

 of the stage and a clamping lever provided. If it is essential that 

 the instrument be more or less portable, it may be so made as to 

 be readily detached from its working foot and transferred to a light 

 folding tripod foot, a smaller travelling case being provided. 



With regard to such details as milled heads, it is worth while 

 remarking that those of the coarse adjustment are commonly placed 

 too near together, and are frequently of too small a diameter. The 

 latter remark also applies to many fine adjustment milled heads 

 since the introduction of the lateral position. 



Some firms appear to be taking up the position that one 



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