become more pronounced and the field smaller as the 

 distance between eye and lens is increased. 



When magnifiers are used on opaque objects 

 those which are not transparent and which are illumin- 

 ated by reflected light not transmitted through them 

 a position should be chosen opposite a window 

 or flame that the greatest amount of light will reach 

 the object. If a hat is worn place it back on the head 

 so that the rim will not cut off the light. 



Holding the object in one hand, take the magnifier 

 between the thumb and forefinger of the other and place 

 the fingers of the hand holding the lens in such a manner 

 that they shall rest upon the other hand, thus insuring 

 steadiness of the lens and object and adding consider- 

 ably to the comfort of working. 



While it seldom occurs that magnifiers are made 

 with other than double convex surfaces, single achro- 

 matic lenses with plane convex surfaces are sometimes 

 used. These should be used with their convex sur- 

 faces toward each other. 



In magnifiers containing several lenses, when they 

 are used together, the one of highest power should be 

 nearest the object. 



When reversed the angular field is greater, but the 

 spherical and chromatic aberrations are correspondingly 

 greater. 



22 



