130 ACCESSORY APPARATUS. 



the platform, to bring the platform itself into its fixed place on the 

 traversing plate below, and then to adjust the traversing plates 

 themselves by their respective scales. Even a non-movable stage 

 may have a similar pair of scales adapted to it ; the vertical scale 

 being so placed, as to mark the position into which the object- 

 platform is brought by sliding it up or down ; and the horizontal 

 scale being marked upon the object-platform itself, so as to allow 

 the observer to note the precise position of the end gf the glass 

 slide. Thus let it be supposed that, by shifting the slide from 

 side to side, and by moving the object-platform up or down, a 

 certain object has been brought into the field ; if the place of 

 the object-platform and of the slide be then noted by the vertical 

 and the horizontal scales, the object may be found at any fature 

 time without difficulty, by readjusting the slide and the object- 

 platform to the same numbers.' The numbers referring to each 

 object may either be marked upon the slides themselves, like 

 the names of the objects, or may be recorded with these in a 

 separate list, referring to the slides by figures alone. The gene- 

 ral adoption of such a plan, though involving a little more labor 

 at first, would prove in the end to be a great saving both of time 

 and trouble. 



54. Magnetic Stage. — If a stage be unprovided with a travers- 

 ing movement of any kind, there is no means of allowing the 

 object to be moved in all directions with smoothness and facility, 

 and yet of holding it in any position in which the Microscopist 

 desires to retain it, more convenient and more ready of applica- 

 tion, than is furnished by magnetic attraction. A magnetic 

 stage was originally proposed by Mr. King of Bristol ; but seems 

 to have been first brought into efficient practical action by Mr. 

 G. Busk. His plan consists in attaching two semicircular mag- 

 nets to the under side of the stage, so as nearly to surround its 

 aperture, and in inserting, for the conveyance of the magnetic 

 force to the upper side, four soft iron pegs, which slightly pro- 

 ject above its surface ; over these an object-bearer of soft iron, 

 with its under surface ground smooth and true, will slide so 

 readily, as to admit of very easy and precise adjustment of the 



' The first of the above plana, to the utility and accuracy of which the Author can 

 bear strong testinnony, was suggested by Mr. Okeden in the " Quart. Microsc. Journal," 

 vol. iii, p. 166. The second had been previously suggested by Mr. E. G. Wright in the 

 same Journal, vol. i, p. 302; the descriptions of Ijoth are made clear by figures. Other 

 " finders" are described and figured by Mr. J, Tyrrel, Mr. T. E. Amyot, and Mr. Bridg- 

 man, at pp. 234 and 302-304 of the last-named volume. It appears to the Author that 

 Mr. Olteden's plan might be adopted with very little trouble or expense in every Mi- 

 croscope possessed of a stage movement, and Mr. Wright's in every Microscope with a 

 fixed stage but movable object-carrier; and that it would be very desirable for eetry 

 microscope thafmay be made hereafter, to be furnished with sucli scales. If the dif- 

 ferent makers could agree upon some common system of graduation, in the same way 

 as Microscopists have adopted 3 inches by 1 as the standard dimension of object- 

 slides, much trouble would be saved to observers at a distance from one another, who 

 might wish to examine each others' objects ; for the numerical reference attached to 

 each object would then enable it to be found by every observer, whose stage should be 

 graduated upon the same method. 



