ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



305 



into a Dissecting Microscope, as shown in fig, 46. It is for this 

 use of the instrument that the stage is made to move up and down by 

 rack and pinion, so as to form a fine adjustment.* 



Helmholtz's Vibration Microscope.t — Professor H. L. F. Hclm- 

 holtz's instrument (fig. 47) is thus described by him. 



Fig. 47. 



" No complete mechanical theory can yet be given for the motion 

 of strings excited by the violin bow, because the mode in which the 

 bow affects the motion of the string is unknown. But by applying a 



* Tlie Microscope is briefly described in Arch. Sci. Phys. et Nat., xiv. (1885) 

 p. 575, but the above figs, are taken from photographs kindly sent us by 

 Prof. Fol, 



t Helmholtz, H. L. F., ' On the Sensations of Tone as a Physiological Basis for 

 the Theory of Music,' 2nd Eng. ed. by A. J. Ellis, London, 1885, pp. 80-2 

 (2 figs.). ' Die Lehre von den Tonempfindungen,' 4te Ausg., Braunschweig, 

 1877, pp. 137-41 (2 figs.). 



Ser. 2.— Vol. VI. X 



