MICROSCOPIC OBJECTS. 



7 



make, or have made the simpler arrange- 

 ment represented below. As will be seen, 

 it consists of a series of boxes fitting into 

 each other after the fashion of a sliding body 

 camera. It can easily be lengthened or 

 shortened by the addition or removal of one 

 or more boxes. Any joiner could easily 

 construct such a camera on seeing the il- 

 lustration. 



Double dark slides may be employed, if 

 well made, but a single slide is better, as 

 the focussing glass can be placed in it, and 

 when replaced by the sensitive plate the 

 latler will lie in exactly the same place, 

 which is of vital importance. For low 

 powers, very fine ground glass will answer, 

 but for higher powers plain glass is best. 



In this case the image must be examined by 

 means of a focussing eye- piece. The fol- 

 lowing excellent mode of performing the 

 difficult operation of focussing is given by 

 Mr. G. E. Davis, in " Practical Micro- 

 fcopy :" " Removing the ground glass slide, 

 another is substituted of mahogany, but 

 pierced with a series of seven holes, into 

 each of which the ordinary A eye-piece may 

 be fixed. The thickness of the slide is such 

 that when the eye piece is pushed in as far 

 as it will go, the diaphragm lies in the same 

 plane as the ground surface of the glass 

 slide. To anyone accustomed to focus by 

 the old method, the present system will be 

 found a considerable improvement, it being 

 easy under these conditions to obtain a 



sharp focus with an ordinary paraffine lamp 

 when using the objective." 



When the camera is extended only a short 

 distance, the hand will be able to reach the 

 coarse or fine adjustments of the micro- 

 scope; but when drawn out to three feet 

 or fi)ur feet, this will be impossible. It 

 then becomes necessary to provide some 

 method by which focussing can be easily and 

 exactly performed while viewing the image 

 on the screen, the camera being extended. 

 Procure a hollow brass rod, \ inch in diam- 

 eter, and the length of the base-board. Fix 

 it to the side of the board by metal " eyes," 

 so that the rod may revolve somewhat stiffly ; 

 if the camera be supported on trestles, the 

 rod may be fixed under the base-board, which 

 is more convenient. Make a grooved wood- 

 en wheel, tao inthes diameter, and fasten 



it to the rod, so that it will be opposite the 

 fine adjustment of the microscope when the 

 latter is placed horizontally, with the eye- 

 piece end fitted to the camera front. Make 

 an endle?s band of narrow tape, of such a 

 length that it will pa=s over the grooved 

 wheel and the fine adjustment rather tight- 

 ly. On turning the extremity of the rod, 

 the fine adjustment will be moved with suf- 

 ficient slowness and accuracy to allow of 

 correct focussing with a lens of high power. 

 The writer has long used an arrangement 

 of this sort when photographing diatoms, 

 and found it answer admirably. 



The remaining photographic apparatus 

 will be as follows : A macintosh focussing- 

 cloth; ebonite or glass dishes for develop- 

 ing and fixing negatives; glass measures, 

 say 2-oz., 40Z, and 6 oz. capacity; ba>ins 



