ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



799 



slightly varied, which makes the position of the images identical. There 

 are also stops to limit at pleasure the movement of the prism. 



By turning the prism by the milled head at U the image is transferred 

 instantaneously from one tube to the other. 



1 hope that the new arrangement will render good service to the 

 laboratories where microscopical anatomy is taught." 



In some of the earlier forms of Stephenson's Binocular Microscope the 

 upper prism box was made to rotate on the optic axis, carrying with it the 



Fig. 205. 



HAKTING'S QUADRI0CT7LAR MICROSCOPE. 



body-tubes, so that a circle of observers could view the object successively. 

 Prof. Thury's plan, however, avoids the loss of time involved in swinging 

 the tube round, and, what is more important, especially in the case of 

 moving objects, in readjusting the focus for each observer. 



Ahrens's Triocular Microscope. — We cannot be sure that we fully 

 appreciate the rationale of this instrument made by Mr. C. D. Ahrens 

 (fig. 206), but it seems none the less necessary to notice it here if we are to 

 maintain our original intention of recording such designs as have been con- 

 sidered sufficiently practical to be actually manufactured. Moreover, all 

 classes of scientific bodies — zoologists, botanists, horticulturists, medical 

 men, &c. — exhibit and record the abnormalities of their respective branches. 



The Microscope consists, as will be seen, of a stand with three bodies 



3 G 2 



