102 



CONSTRUCTION OF THE MICROSCOPE. 



FIG. 21. 



this country. Those, however, who are carrying on researches 

 upon objects too minute to make this objection felt (such, for 

 example, as urinary deposits), and who need high magnifying 

 powers, without requiring these to possess the greatest attainable 

 perfection, will find this Microscope extremely well suited to 

 their wants. Another instrument constructed by M. Cachet 

 upon the same general plan, but upon a larger scale, is capable 

 of being fitted with Achromatic condenser, Polarizing apparatus, 

 Micrometer eye-piece, Stage movements, &c. ; in the arrange- 

 ment of which accessories, much skilful contrivance is shown. 



The Binocular Microscope of the 

 same ingenious Optician will 

 be described further on ( 40). 

 34. Smith and Beck's Stu- 

 dent's Microscope. Of the pat- 

 terns yet devised for a micro- 

 scope of simple construction, 

 which shall yet be capable of 

 answering every essential pur- 

 pose whether of display or of 

 investigation, that of Messrs. 

 Smith, and Beck appears to 

 the Author to be (to say the 

 least) among the best; and he 

 recommends it with the more 

 confidence, since he has for 

 many years employed one of 

 these Microscopes as his own 

 ivorking instrument. There 

 is nothing distinctive in the 

 tripod support, or in the mode 

 in which the microscope itself 

 is suspended between the up- 

 rights. But the "body" rests 

 for a great part of its length 

 upon a "limb" of solid brass, 

 ploughed into a groove for the' 

 reception of the rack which is 

 attached to the body; this 

 groove being of such a form, 

 that the rack is firmly held in 



it slides SlllOOthly 



Smith and Beck's Student's Microscope. 



through it. The great advan- 



tage of this method of construction over any other in which the 

 rack-and-pinion movement is made to act directly on the body, is 

 that it renders impossible any of that twist which tends to throw 

 the object more or less completely out of the field, and secures 

 that exact centering which is essential to the optical perfection of 

 the instrument. The upper end of the body is furnished with a 

 " draw tube," by which its length can be increased ; and one side 



