NACHET 8 MICROSCOPE. 



101 



EIG. 20. 



hold one end of the slip of glass whereon is placed the object 



under examination, whilst one of the other fingers of each 



hand is used to push up the 



head at the end of the pin, 



so as to lift the tongue from 



the stage ; the slip of glass 



can then be moved from side 



to side, or up and down, 



with the most perfect free- 



dom, and may be firmly se- 



cured at any point by ceasing 



to press upon the heads of 



the pins, which will then be 



forced down by the springs, 



so as to bring the tongues to 



bear on the slip of glass. 



When the microscope is used 



in a vertical position, for the 



examination of urinary de- 



posits, &c., no means of fix- 



ing the object being requir- 



ed, it is convenient to turn 



the tongues backwards, so 



as not to occupy any part of 



the stage. The advantages 



of this arrangement are the 



perfect freedom with which 



the slip of glass can be moved 



under the objective, either in 



finding a minute Object, Or Nachet's Compound Microscope. 



in examining the surface of a larger one ; and the facility and 

 exactness with which it is retained at any point, at which it may 

 be desired to fix it. The disadvantages are, the necessity of 

 using both hands to move the object ; and the interference of the 

 tongues with the movement of the object from side to side, when 

 it is large enough to require a considerable range ; on which 

 last account the plan is unsuited to the use of an aquatic box. 

 The stage is furnished on its under surface with a diaphragm 

 plate, not mounted as a wheel, but sliding in a straight line, 

 which is a less convenient arrangement ; and to its lower side is 

 also attached a stem that carries the mirror, the distance of which 

 from the stage is not capable of variation. This instrument is 

 distinguished by its simplicity and cheapness, and by its adapta- 

 tion to many of the wants of the scientific inquirer. 1 One of its 

 chief disadvantages is the small size (especially the narrowness) 

 of its stage, which cramps the operations of the observer ; and 

 hence it will not be found nearly so convenient to the young 

 microscopist, as the equally simple patterns in common use in 



1 With three objectives and three eye-pieces, giving a range of magnifying 

 from about 50 to about 500 diameters, it is sold in Paris for 190 francs. 



powers 



