30 WHEN TO USE THE MICROSCOPE. 



view distinctly any distant object, to distort my eyes 

 somewhat to the shape of ill-formed button-holts 

 puckered in the sewing. Some individuals, I am 

 aware, foolishly affect this appearance, from the notion 

 that it exhibits an outward and visible sign of their 

 inward profundity of character. In my own case 

 this result may have arisen from my having worked 

 principally at night or in the dusk. ' As to the 

 sight being injured by a continuous examination of 

 minute objects/ writes Mr. Clark, a most scientific 

 naturalist, ' I can truly say this idea is wholly with- 

 out foundation, if the pursuit is properly conducted ; 

 and that, on the contrary, it is materially strength- 

 ened by the use of properly adapted glasses, even of 

 high powers ; and in proof I state, that twenty years 

 ago I used spectacles, but the continued and daily 

 examination of these minutiso (foraminifera) has so 

 greatly increased the power of vision, that I now 

 read the smallest type without difficulty and without 

 aid. The great point to be attended to is not to use 

 a power that in the least exceeds the necessity ; not 

 to continue the exercise of vision too long, and never 

 by artificial light ; and to reserve the high powers 

 of certain lenses arid the microscope for important 

 investigations of very moderate continuance. The 

 observant eye seizes at a glance the intelligence 

 required ; whilst strained poring and long optical 

 exertions are delusive and unsatisfactory, and pro- 

 duce those fanciful imaginations of objects which 



