CONSTRUCTION OF THE MICROSCOPE. 55 



diameter, suitable for Sections of Wood and other like objects viewed with 

 the low-power objective. The powers usually supplied are a separating com- 

 bination of 2 inch and 1 inch, which, by the use of the two eye-pieces and 

 the draw-tube, gives a range of magnifying power from 15 to 110 diame- 

 ters; and a 1-itli inch of 70 aperture, from which, by the same means, 

 a range of magnifying power can be obtained from 140 to 450 diameters. 

 The aperture of the stage is furnished with a cylindrical fitting, which 

 carries two diaphragms (one with a small aperture, the other with a 

 larger) for regulating the quantity of light reflected from the mirror to 

 the object, a ground-glass for the equable diffusion of the light over a 

 large field, and a ' spot-lens ' for black-ground illumination. The mir- 

 ror is plane on one side, and concave on the other; and a condenser for 

 opaque objects is attached by a jointed arm, giving universal motion, to 

 the tube that carries the body. The Objectives of this Microscope, as of 

 most of those constructed by the same Makers, are made to fit into the 

 nozzle of the body by their '' patent sliding adapter/ which enables one 

 power to be exchanged for another without any screwing or unscrewing. 

 But their Microscopes can be used with any objective carrying the 

 ' Society's screw/ by simply unscrewing the special nozzle from the end 

 of the body. And by sliding the special nozzle upon either of its own 

 objectives, this may be used with any other instrument furnished with 

 that screw. 1 



Students' Microscopes. 



54. The principle is now universally recognized, that the form of 

 Microscope best adapted to the wants of the Medical or Biological Stu- 

 dent, is one in which simplicity and compactness of general construction 

 are combined with excellence in optical performance. The demand for 

 instruments of this kind was first met by Continental Opticians; and at 

 the time when Messrs. Ross, Powell and Lealand, and Smith and Beck 

 then almost the only constructors of Microscopes in this country sold no 

 Objectives but such as would stand the highest tests and were costly in 

 proportion, recourse was necessarily had, by such as desired simpler and 

 cheaper instruments, to the Opticians of France and Germany; among 

 whom MM. Nacliet, Oberhauser (succeeded by Hartnack), and Kellner 

 (succeeded by G-undlaeh), long shared the chief English demand. A 

 large number of new Makers, however many of them trained in one or 

 other of the three principal establishments just named have now entered 

 the field; and have put themselves in fair competition with Continental 

 Opticians, and with each other, alike in the excellence of their work 

 (both mechanical and optical), and in moderation of price. A distinct 

 class of ( Students' Microscopes ' of English construction, more or less 

 framed upon Continental models, has thus come into general use; afford- 

 ing ample choice, in the varieties of their pattern, to such as may have a 

 preference for one or other of them as most suitable to the work on which 

 they may be engaged. With few exceptions, the Microscopes properly 

 belonging to this class have the small short ' body ' (capable, however, of 

 being lengthened by a ' draw-tube ') of the Continental instruments; 

 and this is grasped by a tube attached to the ' limb/ in such a manner as 



1 The price of this Microscope with the above-named Accessories, in a well- 

 made mahogany Case, is 6 10s. An Objective of l-6th inch focus, giving a max- 

 imum power of 560 degrees, or one of l-7th inch giving a maximum power of 700 

 diameters, may be substituted for the l-4th inch at a very small advance of cost. 

 A Polariscope and Achromatic Condenser can be easily added. 



