Ch. Ill] 



BINOCULAR MICROSCOPES 



87 



monocular microscope, it seems that the argument that the eye should 

 be in a condition of rest and not of accommodation when doing micro- 

 scopic work, that is, the argument for the parallel tubes, seems con- 

 vincing. Perhaps the Yankee spirit of compromise will be found most 



Fig. 54-55. 



Object 



Prism Arrangement for Two 

 All Powers. 



Object 



Forms of Binoculars for 



(Conrad Beck, Jour. Roy. Micr. Soc. 1914). 



In fig. 54 the arrangement is for parallel tubes, and in fig. 55 for converging 

 tubes. 



Object The object. 



Ob The objective. 



/, r; /, r The right and left beams of light emanating from the same point 

 of the object. 



As these beams extend through the objective and into the prisms they are 

 equally divided so that half the right beam goes to the left and half to the right 

 eye, and so with the left beam. This is indicated by the heavy and light 

 broken lines by which the two beams are indicated. 



/, 2, 3, 4; 1, 2 The four prisms in fig. 54, and the two prisms in fig. 55. 

 The prisms are of the necessary length to make the optical path of the light 

 equal for the two tubes, hence the magnification is equal for the two eyes. 



truly practical in this matter and the binocular tubes of the future 

 will be neither parallel nor too convergent. 



§ 145. Dissecting spectacles. — Various devices have been pro- 

 duced from time to time to connect directly in some way with the eye. 

 The long-used watchmaker's or jeweler's eye glass is the most familiar 

 example, and answers fairly well, although for most dissecting work it 



