198 



Mr. C. Tomlinsou 



one portion of each radius, the compensating interference 

 of the two contiguous systems of undulations is so exactly 

 balanced, that the surface remains smooth and unruffled, 

 and greatly adds to the symmetrical effect of the whole. 



86. It is a necessary consequence of the last observation, 

 that if the eye deviate from the perpendicular view of the 

 mercurial surface, the form of the figure will vary accord- 

 ing to the angle of deviation, and, thus present such diver- 

 sity of form, that, were it not for the absence of colour, we 

 might almost draw an analogy between the mercurial figures 

 and those of the ever-varying kaleidoscope. 



87. The convexity of the mercurial surface has consider- 

 able influence upon the figure, and as a small surface of 

 mercury is comparatively more convex than a larger sur- 

 face, a smaller or a larger glass presents an interesting 

 change in the figure. 



88. Thus, in a goblet smaller than the one previously 

 used (82), sufficient mercury was poured in to produce the 

 note G, when a figure resembling the figure 3 was presented. 



Fig. 3. 



In this case as in the former the outlines of the figures are 

 formed by a change in the direction of the undulae, and 

 receives many pleasing modifications by varying the angle 

 of observation. 



89. It appears, as indeed it is reasonable to suppose, that 

 the alteration produced in the figure, by varying the size of 

 the vessel, is also produced, in nearly the same degree, by 

 employing various depths of mercury in an inverted conical 

 or dome-shaped vessel, the proportion between the chord 



