ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



307 



the ratio of the pitch numbers of the observed body and of the 

 fork differs too much from one expressible by small whole numbers, 

 the motion of the curve is too rapid for the eye to follow it, and all 

 becomes confusion. 



If the Vibration Microscope has to be used for observing the motion 

 of a violin string, the luminous point must be attached to that string. 

 This is done by first marking the required spot on the string with 

 ink, and, when it is dry, rubbing it over with wax, and powdering 

 this with starch so that two or three grains remain sticking. The 

 violin is then fixed with its strings in a vertical direction opposite the 

 Microscope, so that the luminous reflection from one of the grains of 

 starch can be clearly seen. The bow is drawn across the strings in a 

 direction parallel to the prongs of the fork. Every point in the string 

 then moves horizontally, and on setting the fork in motion at the 

 same time the observer sees the peculiar vibrational curves already 

 mentioned." 



Reichert's Stand with New Stage and Iris Diaphragm. — Herr 

 C. Eeichert has adapted to this stand (fig. 50) an arrangement for 

 moving the object in two directions, which, like that of Mr. J. Mayall 

 jun., does not necessitate 



any addition to the thick- Fig. 48. 



ness of the stage so as to 

 interfere with the illu- 

 mination. 



The arrangment is 

 shown in fig. 50 in situ, . r 

 and also separately at fig. 

 48. The glass slip is held j|'' 

 between two clips r r. ^ 

 These clips are attached 

 to a nickel-plated frame 

 which slides on the upper 

 surface of the stage, and is 

 secui-ed in place by grooves 



at the side. A projecting tail-piece with a rack on the under side 

 passes through the limb of the Microscope, and the frame is moved 

 from back to front by a pinion in the limb, which is actuated by the 

 milled heads Ji' h'. The motion of the slide from side to side is effected 

 by the milled heads h h, which by 

 means of a screw move the piece to 

 which the clips are attached. The 

 clips consist of two metal plates, with 

 a piece of indiarubber between, slightly 

 projecting laterally, so that the metal 

 is not in contact with the slide. By 

 loosening the screws I I the clips can 

 be brought closer together, so as to 

 grasp the slide tightly, which is thus 

 moved on the surface of the stage without any intermediate support. 



The Abbe condenser is shown in figs. 19 and 50. It is movable by 



X 2 



Fio. 49. 



