420 Mr. Charles Tomlwsons Experiments 



117. The circumstance of two notes so near together 

 as D and E, being produced from one vessel, is, at first 

 view, by no means in accordance with the principles en- 

 deavoured to be established in my last paper on the funda- 

 mental and secondary tones, and nodal divisions of a glass 

 goblet (95 to 115). With earthenware vessels, Mr. Dodd 

 states, that between the two notes produced, he never 

 obtained an interval of more than three semi-tones : — that 

 these two notes occurring alternately at eight distinct 

 points of the vessel, led Mr. Dodd to suppose the existence 

 of eight vertical nodal lines, each of which, separated two 

 vibrating arcs, which produced different notes (75). I 

 have shewn, that in glass vessels, the fundamental tone is 

 always due to a quadripartite division, and that eight 

 divisions produce a note generally in the second octave 

 above the fundamental note : the octopartite division is, in 

 fact, my second secondary tone, and as I could not think 

 but that a certain harmonious relation, both in theory 

 and practice must exist between the modes of vibration in 

 glass and porcelain, &;c. I suspected some fallacy in the 

 theory, which sought to explain the production of the two 

 notes D and E above referred to. I, therefore, proceeded 

 as follows : 



118. I procured a circular block of wood, from the 

 centre of which rose a short cylinder of the same material, 

 two inches in length and one inch in diameter : the top of 

 this cylinder was covered with soft leather, and a female 

 screw passed down it. I then procured a thin wedgwood- 

 ware evaporating dish with a flat bottom and a lip : — the 

 dish was five inches in diameter, and about one inch deep. 

 In the centre of the dish I drilled a hole, through which a 

 thumb screw with a leather collar was passed, and so fixed 

 the dish to the top of the wooden cylinder. In this way 

 the dish was quite firm and secure, and vibration produced 

 no jarring or unsteadiness, and being held in the centre, 

 the tones of the vessel were not damped. 



119. Matters being thus arranged, I vibrated the vessel 

 at four equidistant points of the rim by means of a bow, 

 and obtained E within the stave, and at four other points 

 midway between, I obtained the third below, namely, C. 

 This note C was produced at the lip, at the point opposite. 



