o SELECTION AND TJsE 



proved by a very simple experiment. Place some tine print, 

 such, for example, as the present page, at a distance of six feet 

 from the eye, and gradually move closer to it. At six feet the 

 letters will be indistinguishable; at two feet they will be quite 

 distinct; at one foot still more distinct; at three inches they 

 will be quite blurred. There is, therefore, a limit to the degree 

 of closeness with which we can approach any object for the 

 purpose of examining it, and the object of a microscope is to 

 enable us to get close to it, as it were, without blurring our 

 view. If, without changing the distance of the eye from the 

 paper (three inches) we introduce between the two a lens of one 

 inch focus, and bring it into proper position, we will find that 

 the indistinctness formerly complained of disappears, and the 

 object is now not only seen clearly, but appears very much 

 magnified. That objects appear large in proportion to their 

 nearness to the eye may be thus shown: Take two slips of 

 paper printed with type of the same size (two clippings from a 

 newspaper answer well) and place one at a distance of ten 

 inches from the eye and the other at a distance of five inches 

 the edge of the upper slip being placed so as to lie about the 

 middle of the lower one. In this way we can readily compare 

 the apparent sizes of the type on the two slips, and one will be 

 found to appear just twice as large as the other, though, of 

 course, we have the evidence of our senses to prove that they 

 are precisely of the same size. Moreover, as the usual distance 

 for distinct vision is about ten inches, in persons of middle 

 age, it will be found that a lens which enables us to view any 

 object clearly and distinctly from a distance of one inch, will 

 enable us to see it just ten times larger and ten times more dis- 

 tinctly than we could do when looking at it from a distance of 

 ten inches. A consideration of these facts led the late Dr. 

 Goring to propose the name engiscope as a substitute for the 

 word microscope the word engiscope signifying to see things 

 at a very short distance. 



The facts which we have just detailed must, however, be re- 

 garded as illustrations, rather than explanations of the action of 

 the microscope. It is evident that the power of a lens to in- 

 crease the distinctness with which any object is seen, depends 

 not only upon the action of the lens upon the rays of light, but 

 upon the influence which such modified light exerts upon the 



