MICROSCOPIC ILLUSTRATIONS^ 265 



of instruments by the help of samples of spurious lined 

 objects. 



The art of working metals* and object-glasses is one of 

 extreme delicacy, I know of no parallel to it ; it ought 

 perhaps to be called one of the fine arts, for it ultimately 

 consists in producing, though indirectly, the most exact 

 pictures of objects which the imagination can possibly 

 conceive. No injury, I think, can result to the interest 

 of superior opticians by giving the public the power of 

 perceiving the excellency of their productions. Inferior 

 artists, however, who can produce nothing good, will 

 naturally love darkness rather than light and for why ? 

 truly, because their works are evil. If the public had no 

 certain means of knowing the exact rate of the going of 

 chronometers, how could the makers of them expect to be 

 remunerated for the better sorts according to their real 

 value ? and if a workman is not content to be paid for his 

 instruments according to the quality of them, be it what it 

 may, all that can be said, is, that he must be both a knave 

 and a fool. Very fine optical instruments of all sorts are 

 exceedingly scarce, and ought to be exceedingly valuable, 

 as will be seen hereafter. 



I shall now proceed to lay down certain self-evident 

 propositions relative to the metals and object-glasses of 

 engiscopes, which, simple as they are, will be found 

 sufficient to place the reader in possession of a key to the 

 knowledge of what is good and evil in these instruments. 



1st. In all object-glasses and metals the main body 

 of the light comes from the periphery, and not from the 

 centre; so that if they are divided into a number of 



* This is the technical term for concave speculums. 

 T 



