24 



THE AMERICAN MONTHLY 



=.1 



Receipts for Microscopists.* 



BY JULIEN DEBY, C.E., F.R.M.S. 



All those who have had practice 

 with the microscope have, through 

 personal experience, discovered for 

 themselves some special " dodges " 

 which have facilitated their re- 

 searches, or enhanced the efficiency of 

 their instruments. If such persons 

 would condescend to publish their 

 results in this respect, they would 

 render service to others laboring 

 under difficulties which they have 

 overcome. It is in order to induce 

 members of the Quekett Club to 

 follow my example, that I this day 

 draw their attention to a few simple 

 adaptations of means to ends. 



I. — When allowing all but adepts 

 in the use of the microscope to peep 

 through my high-power glasses, I have 

 often felt a certain degree of uneasi- 

 ness, not to say of alarm, regarding 

 the fate of valuable test-slides, or still 

 more valuable objectives. Many 

 others here present have no doubt ex- 

 perienced the same discomfort which 

 I find an easy matter to attenuate to 

 a considerable extent, by focussing 

 from the eye-piece instead of from 

 the coarse or the slow motion. All 

 that is needed for this is a rack and 

 pinion to the eye-piece of considerable 

 length. An inch or two up or down 

 corresponds here to a fraction of a 

 turn of the fine adjustment of the 

 microscope, so that very little danger 

 exists of any sudden contact with the 

 covering glass. As soon as an indis- 

 tinct view of the object is obtained 

 through the ordinary coarse adjust- 

 ment of the microscope body, the 

 focus is brought to exactness by means 

 of the coarse motion of the eye-piece 

 without much difficulty. For demon- 

 strations or exhibitions in public, 

 microscopes could thus be made with- 

 out the ordinary fine motion. 



II. — When mapping with the micro- 

 spectroscope, the difficulty of mea- 

 suring exactly the position of fine 



*From TAe Journal of the Quekett Micro- 

 scopical Club. 



lines or absorption bands is often 

 great, even when using the admirable 

 micrometers invented by Mr, Brown- 

 ing and Mr. Sorby. I find that in 

 most practical cases the micro-spect- 

 rum can be thrown upon a sheet of 

 white paper by means of an ordinary 

 camera lucida placed over the eye- 

 piece of the spectroscope. Strong 

 light by means of a condenser has to 

 be thrown through the liquid under 

 examination. By means of an ivory 

 rule, finely divided, and brought back 

 to a known line, say D, all other lines 

 or bands may be directly measured 

 off on the rule, and, if desired, the 

 exact results in millionths of a milli- 

 metre may then be computed by any 

 of the known interpolation formulae, 

 such as are given in Suffolk's useful 

 little book.* 



III. — The arrangement of small 

 microscopic objects, such as diatoms, 

 foraminiferse, etc., on slides in regular 

 lines, circles, or patterns, can be much __ 

 facilitated in the following way : — fll 

 Draw with a pen and ink cross lines, "■ 

 or circles, or any other figure required 

 on the surface of the plain mirror of 

 the microscope ; then focus down 

 until the image of these lines is seen 

 on the upper surface of the top lens 

 of the condenser. By means of a 

 mechanical finger, or of a steady hand 

 with a rest, no difficulty will now be 

 experienced in placing the objects in 

 perfectly regular order. 



IV. — I now obtain excellent con- 

 densed monochromatic light by means 

 of a bull's-eye of unusual external 

 shape, the internal portion of which, 

 however, is filled with glycerin or oil 

 of cloves colored to suit. This bull's- 

 eye has a plane back and a concavo- 

 convex front, and the liquid is intro- 

 duced through a hole in the flat side, 

 closed by a small ground stopper. 

 This apparatus is furnished with uni- 

 versal motions, and has a rack and 

 pinion foot. It was made for me by 



*Spectrum Analysis as Applied to Micro- 

 scopical Observations, W. T. Suffolk, F.R. 

 M.S. London, John Browning, 6j}, Strand 

 1873. 



