110 PRACTICAL TREATISE ON THE MICROSCOPE. 



diagonally, a ciirved spring keeping the plate in contact with 

 the screws. This stage has three pieces of brass projecting from 

 its circumference to fit over the edge of the stage-plate of the 

 microscope, and by these it can be so elevated above the stage- 

 plate, as to allow of light being thrown very obliquely under 

 any object, by means of a prism invented by Amici, which 

 will be described in another part of this work. The workman- 

 ship of this instrument is exceedingly well executed, and of 

 the continental microscopes, it is certainly one of the most 

 perfect and complete in aU its parts. The author is indebted 

 to Mr. Warren De La Rue for the loan of the microscope of 

 which fig. 54 is a representation. 



The object-glasses supphed with all the above-described 

 microscopes, except those of Messrs. Powell, Eoss, and Smith, 

 and the lowest, viz., two-inch, one-inch, and half-inch of Mr. 

 Dancer, are all constructed nearly on the same plan, and will 

 be described in the chapter devoted to the "Magnifying 

 Powers." 



Having noticed all the important points in the con- 

 struction of the principal English and foreign microscope 

 stands, whereby great steadiness, accuracy of adjustment, 

 portability, and other valuable requisites have been so suc- 

 cessfully carried out, our attention must now be directed to 

 the apparatus that may be added to any instrument to render 

 it complete for all the purposes of scientific investigation. 



CHAPTER in. 



ACCESSORY INSTRUMENTS. 



Besides the object-glasses, the eye-pieces, and the mirror, 

 together with the parts constituting the stand of a microscope, 

 such as the compound body and the stage, with the supports 

 and adjustments for each, it has been found in practice highly 

 essential that certain other instruments should be supplied. 

 These may be divided into two classes ; first, into those which 



