on Visible Vibration. 195 



78. A large number of figures has been produced by em- 

 ploying one glass as a standard, a soda-water glass, for in- 

 stance, yielding a certain note, which is reduced, at musical 

 intervals, by adding successive quantities of perfectly clean 

 and pure mercury, and the figure is produced by passing 

 the moist finger round the edge of the glass. The figure is 

 then carefully examined and copied ; each figure answering 

 to a certain note or half-note. 



79. Results having been thus obtained, the question 

 naturally suggested itself, whether a certain sound is neces- 

 sarily accompanied by a certain figure 1 It seemed obvious, 

 that when two unisonant glasses were employed together, 

 with the same quantity of mercury in each, that the same 

 figure would be obtained from each. Thus, where two 

 glasses were employed, the fundamental note of each being 

 D sharp, and four fluid ounces of mercury are required by 

 each to lower their respective fundamental notes to C sharp, 

 the resulting figures, both in theory and in practice, are 

 the same. So, also, with a glass, whose fundamental note 

 is C sharp, if mercury be added below the axis (53), the 

 same figure is produced as from the two former glasses ; 

 but we approach nearer the main question when two disso- 

 nant glasses are employed requiring dissimilar bulks of 

 of mercury to accord them. Thus, one set of figures was 

 produced from the surface of mercury contained in a glass, 

 the fundamental note of which, when empty, was D sharp. 

 In order to verify the first set of figures, another glass was 

 taken similar in size and shape to the former, but whose 

 fundamental note was C, differing from the former by 

 three semi-tones. Both glasses were soda-water glasses 

 forming part of my set of musical glasses (47), and they were 

 chosen on account of their affording an extensive mercurial 

 surface, and offering facilities for easy vibration by almost 

 a touch. The bulks of mercury, of course, differed greatly 

 in order to accord the two glasses ; and yet, in many cases, 

 the same figures were obtained from the second glass as had 

 previously been obtained from the first. Thus, D, C sharp, 

 C, B, B flat, G, F sharp and F, middle octave of flute, 

 gave, nearly, and in some cases, exactly, the same figures 

 for each note as in the Hist set, aud, in all cases tbe dis- 



