165 



*' Receipts for Microscopists." 

 Bj JuLiEN Deby, C.E., F.R.M.S. 



(Read June 2oth, 1880.) 

 PLATE XII (Lower Part.) 



All those wlio Lave had practice with the microscope have, through 

 personal experience, discovered for themselves some special " dodges' 

 which have facilitated their researches, 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 

 labouring under difficulties which they have overcome. It is in 

 order to induce members of the Quekett Club to folloAV my 

 example, that I this day draw their attention to a few simple adap- 

 tations 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 uneasiness, not to say of alarm, regarding the fate of valu- 

 able test-slides, or still more valuable objectives. Many others here 

 2)resent have no doubt experienced 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 cover- 

 ing glass. As soon as an indistinct view of the object is obtained 

 through the ordinary coarse adjustment of the microscope body, 

 the focus is brought to exactness by means of the coarse motion of 

 the eye-piece without much difficulty. For demonstrations or ex- 

 hibitions in public, microscopes could thus be made without the 

 ordinary fine motion. 



II. — When mapping with Micro-spectroscope, the difficulty of 

 measuring exactly the position of fine lines or absorption bands is 



