104 



CONSTRUCTION OF THE MICROSCOPE. 



Student's Microscope ; but the stage is much longer froni back to 

 front, so as to give more room ; and from the back of it rises a 

 strong curved limb for the support of the body, which is made to 

 slide upon it, as in the previous case, by a rack-and-pinion move- 

 ment. A second milled head is seen above that by vs^hich the 

 focal adjustment is made; and this acts by means of a rack 

 upon the dr^vir-tube, vrhich it brings out or shuts in, without the 

 necessity of holding the body with the other hand, — a movement 

 which will be found of very great advantage, when the " erecting 

 Pig 22. ■ eye-piece" (§ 44) is employed 



for varying the magnifying 

 power. The chief use of 

 this erecting eye-piece, which 

 screws into the lower end of 

 the draw-tube (Fig. 32), in the 

 Dissecting Microscope, is to 

 erect the image (as its designa- 

 tion implies), and thus to facili- 

 tate the employment of dissect- 

 ing instruments upon an object 

 under inspection, the selection 

 of minute shells, &c., or other 

 manipulations, which cannot 

 be so conveniently carried on, 

 save after long practice, when 

 the object is inverted. As the 

 "fine" adjustment cannot, in 

 this pattern, be applied to the 

 "limb," it is attached (if re- 

 quired) to the lower end of the 

 body itself, as in Messrs. Smith 

 and Beck's larger Microscope 

 (Fig. 29) ; but for the purposes 

 to which such an instrument 

 as this is usually applied, the 

 fine adjustment is seldom need- 

 ed, the rack-movement being 

 sufficiently exact and sensitive 

 to furnish all that is needed 

 for low and medium powers. 



the Physiologist and Medical Practitioner, without exceeding ten pounds in price. To 

 tliose, however, who, though obliged to limit their first outlay, contemplate making sub- 

 sequent additions, the Author would strongly recommend the choice of the instrument 

 described in the text, as one on which such additional expenditure may be more pro- 

 fitably bestowed. Since the above were written, Messrs. Smith and Beck have brought 

 out the "Educational Microscope" there alluded to; and after a careful examination of it, 

 the Author can strongly recommend it as admirably adapted to the purposes for which 

 it is intended. It is fitted with two eyepieces and two objectives, giving a range of 

 powers from 55 to .350 diameters; and may also be furnished with an extra low power 

 for large opaque objects, at a small additional cost. For the additional sum of £5, a Lie- 

 berkUhn, Parabolic Illuminator, Polarizing Apparatus, Camera Lucida Prism, Aquatic 

 Box, and Zoophyte Trough are supplied ; all fitted into the same very portable case, and 

 rendering the instrument extremely complete. 



