to the construction of microscopes consisting simply of a body 

 with its adjustments for focussing arranged on the simplest 

 kind of a support usually a rod and foot somewhat like a re- 

 tort stand. Such microscopes have been used largely for exam- 

 ining objects in aquaria, and hence the name. They are also 

 applicable to the examination of writing, the sheet of paper 

 being simply spread out on a table and the microscope placed 

 on it ; to the examination of portions of the surface of the 

 human body in various cases of skin disease, and, in short, to 

 the examination of any object which cannot be conveniently 

 placed on the stage of an ordinary microscope. 



Microscopes for Special Purposes. In addition to 

 the microscopes which we have described, some of which have 

 been devised with a special view to certain particular lines of 

 research, it often happens that a microscope is needed for a 

 single purpose, and for no other. Thus, for example, in Ger- 

 many, a few years ago, microscopes were made and sold for the 

 sole purpose of examining flesh for trichinae. These micro- 

 scopes were very simple, and when their quality was considered, 

 they were very cheap^-the cheapness being due, in a great 

 degree, to the fact that no provision had been made for a 

 multiplicity of conveniences, which, in the case of these special 

 instruments, would never be of any use. As the microscope 

 becomes more generally used, and the people at large become 

 more thoroughly acquainted with the extraordinary aid which 

 it is capable of rendering to those who are engaged in the arts, 

 it is probable that the numbers of these cheap microscopes will 

 increase, in which case we may expect to see the price greatly 

 reduced in proportion to the quality. 



" Class" Microscopes.- When a number of objects are 

 to be shown to a class or to a scientific meeting, it is desirable 

 to avoid the inconvenience arising from each individual having 

 to go to the instrument, and this is unavoidable where ordinary 

 microscopes are used on fixed tables. Prof. Quekett got over 

 this difficulty by having his class-room or theatre fitted up with 

 rails upon which the microscopes with their lamps were passed 

 from one to another, and where the company is small, the com- 

 mon revolving table meets every requirement. But where the 



