126 MICROSCOPIC ILLUSTRATIONS. 



The achromatic will be distinguishable from the single 

 lens by its exceeding penetration, and by the total free- 

 dom from spherical and chromatic aberration with 

 which the light is transmitted through it. It is true 

 that if the common lens have a diaphragm to limit its 

 aperture, the vision will be more distinct, and the light 

 less coloured ; but then, compare the two again, and in 

 the case of the single lens there will be a perceptible 

 diminution of light, and the eye will soon grow weary in 

 endeavouring to trace out the minutire of an object. 



SECT. 8. Garden Clamp for the Microscope. This piece 

 of apparatus enables us to employ the microscope for 

 the examination of flowers and plants in the garden or 

 greenhouse. The clamp is represented by the annexed 

 engraving, fig. 28. The end, c, may be screwed to a 



Fig. 28. 



tree, door-frame, or any other convenient place. The 

 body of the microscope is then inserted into it at a, and 

 fixed there by the pinching screw, b. To the lower end 

 of the body is screwed a small arm, constructed for the 

 purpose, arid carrying the forceps for holding the object. 

 The object-glasses, A, with their silver specula, are the 



