I0:t MICKOSCOPF.S FOB 



is neoessar}*, I Trould recommend obseiTcrs, when requiring it of great 

 intensity, to employ reflection for condensation, and not obtain their 

 condensation by refraction. On this account I prefer the ingenious 

 paraboKc reflector of Mr. "Wenham (see Micrograplm, p. 88. fig. 8)^ 

 or the same in solid glass as contrived by ls\x. Shadbold. The beautiful 

 oblique prism of M. Natchet, has many useful properties, still on 

 principle all condensation by refraction should be avoided. "When 

 the construction of the microscope will admit of a "wax taper to 

 be placed close behind the object, which those described in the 

 " Microscopic Illustrations" do, very pure vision is obtained. 



Another point of some imj)ortancc in the examination and verifica- 

 tion of striated objects is the power of making them revolve in the 

 axis of the optical part of the microscope. This is efi'ected both in 

 Dr. Gorings Engiscope and in mine. To obtain this pm'pose, it is 

 necessary that the moveable stage be attached to a fix;ed ring, so that 

 the motions, however eccentric they may place the slides, shall 

 always keej) the object in the centre of revolution. 



For viewing animalcules in phials or glass tubes, there is no method 

 so good as that of placing the phial itself in the spiiag pliial holder, 

 having fii'st tiuTied the microscope on its side, as shown in the 

 Micromopie inustrations, figure 21. A microscope that has not the 

 necessaiy motion for this purpose, cannot do its work effectually, 

 therefore all large instruments should possess it. 



In a large microscope, which is a great luxury always to have at 

 hand, I find it ad\T.sable to have it eqmpped with two ackromatic 

 bodies — a large body for shallow magnifying powers, and a small one 

 for high powers. 



The magnifying powers of a complete microscope for perfectly 

 examining all kinds of Infusoria should range fi'om 50 to 1000 

 diameters; and as this cannot be obtained with first-rate glasses, 

 without rccoiu'se being had to several sets, such an instrument would 

 be necessarily expensive. The microscope first mentioned has two or 

 thi'ee sets of glasses, varpng fi'om 35 to 800 ; and the second, one 

 set, from 100 to 250 diameters ; so that, as before stated, all the 

 most intei'csting observations on Infusoria may be conducted with 

 either of these iusti-uments, whilst additional sets may be obtained 

 as occasion requu'cs. 



It is important to notice, that in all cases where the magnifying 



