CONSTRUCTION OF THE MICROSCOPE. 



53 



after a better one lias been acquired. Microscopes, of whatever Class, 

 should be provided with the ' Society's screw ' now used not only by 

 British and American, but also by several Continental Makers; so that 

 any of their. Objectives may be fitted to them. (See Note, p. 58.) 



Educational Microscopes. 



51. Field's Educational Microscope. This instrument is known as 

 the ' Society of Arts Microscope/ in consequence of its having gained the 

 medal awarded by that Society, in 1855 (at the suggestion of the Author) 

 for the best three-guinea Compound Microscope that was then produced. 

 It has two Eye-pieces, and two achromatic Objectives, Condenser, Live- 

 box, etc., and retains its place amongst useful instruments of low price. 

 It is within the knowledge of the Author, that the production of this 

 instrument has greatly promoted the spread of Microscopy among many 

 to whom the pursuit has proved most valuable as a refreshing and elevat- 

 ing occupation for hours that might have been otherwise either spent in 

 idleness or turned to much worse account. 



52. Crouch's Educational Microscope. This is a very simple and at 

 the same time serviceable, instrument (Fig. 38); well suited for the dis- 

 play of Botanical objects, small Insects or parts of larger ones, Zoophytes 

 and Polyzoa that may be picked up on almost any sea-shore, or the Cir- 

 culation in a Frog's foot. In order to minimize its cost, the ordinary 

 modes of focal adjustment are dispensed with; the ' coarse ' adjustment 

 being made by sliding the body 



through the tube which grasps 

 it, and which is lined with velvet 

 to secure a smooth and equable 

 ' slip;' and the ' fine ' by slight- 

 ly drawing-out the Eye-pieces. 

 This method answers very well 

 for the low powers for which this 

 instrument is intended; and it 

 has the advantage of not allowing 

 the adjustment which a Teacher 

 has made, to be readily disturbed 

 by the Pupils to whom an object is 

 being exhibited. It is provided 

 with a side-condenser for illumi- 

 nating opaque objects; and with 

 a diaphragm-plate fitted into a 

 tube which is screwed into the 

 aperture of the stage, and which 

 is adapted also to receive a po- 

 larizing prism and spot-lens. ' 



53. Parkers Educational 

 Microscope. Such as desire a 

 large and more substantial in- 

 strument, which may be advan- 

 tageously used for higher pow- 

 ers, and made to serve a greater 



variety of purposes, will find the Crouch's Educational Microscope. 



Microscope represented in Fig. 



1 The cost of this instrument, with a dividing object-glass of j inch and 1 inch 

 focus, in mahogany case, is only 2 10s. 



