172 



BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



held for viewing any object, and is well suited for viewing 

 daguerreotypes. Price, 75 cts. 



Fig - 668 ' Double Lens Hand 



Microscope, or Doublet. 

 (Fig. 668.) This is 

 the most powerful in- 

 strument, for the price 

 that it is sold for, that 

 is to be obtained. It consists of two plano-convex lenses, 

 with the plane surfaces outwards, mounted in cells and 

 screwed in a frame having an ivory handle ; where a person 

 has skill to use a great power, this is a desirable instrument. 

 The cut represents the size of the article. Price, $1.00. 



Fig. 669. 



The above cut (Fig. 669) represents the same article of a 

 larger size, not having so great a magnifying power, but a 

 greater field of vision ; it may be used with one lens only, 

 by unscrewing the other. 



Price, in brass mounting, $0.75. 

 " in German silver, $1.00. 



- 670. Stanhope Lens. (Fig. 670.) 



This simple but very powerful lens 

 is the invention of Lord Stanhope ; 

 both ends are ground convex, the 

 one next the eye rather more so 

 than the other. It has many advantages over the common 

 lens : for instance, the difficulty of holding the hand steady 

 to the focus, and the loss of light and field attendant on 

 viewing with a high magnifying power, are here obviated ; 

 for, the length of the cylinder being the exact focus, the 

 object has only to be placed upon the end that is ground 

 less convex, or to be brought in contact with it, when the 



