22 



The Use of a Simple Microscope. 



found to be injurious to the sight, because the eye 720^ used always 

 suffered more or less from the stimulus of light not being applied 



to it in the same manner and 

 degree as to its companion. In 

 the Binocular, as its name im- 

 plies, both eyes are used, and 

 the former drawback is over- 

 come. The beam of light 

 going from the object A to the 

 picture B is divided by a glass 

 prism placed half way across it, 

 into two portions, one of which 

 goes on as formerly, but the 

 other is diverted and sent up a 

 second tube attached to the first 

 tube, forming a V, and thus 

 two pictures, one for each 

 eye, are formed and both eyes 

 are stimulated equally. (See 

 Fig 20). 



Next in importance to the 

 optical part, or magnifying- 

 glasses, is the stand, or frame- 

 work carrying the glasses, by 

 means of which the objects to be 

 examined are held and adjusted 

 for vision. Strength, steadiness, 

 and free movement are essen- 

 tial. Freedom from tremor is 

 absolutely indispensible, for 

 upon this depends much of the 

 comfort in observing, as well 

 as the possibility of seeing at 

 all, with the higher powers, any 

 vibration tending to render the 

 object indistinct. 



One of the most substantial, 

 and most complete is the No. 1a, 

 stand of Mr. T. Ross (Fig 21), 

 which for excellence of work- 

 manship and elaborate finish is 

 scarcely equalled. It was ori- 

 ginally devised with the espe- 

 cial aim of attaining steadiness and freedom from tremor, 

 which it most effectually accomplishes. This is a large and 

 massive as well as an expensive instrument, but where it can 



Fig. 20. 



