494 Lord Kelvin on Continuity in Undulatory Theory of 



bution of induction is precisely the same as in the cases where 

 the field was uniform. The results in Table I EI. also agree 

 with those obtained from specimens in a uniform field. 



Symbols used in Table*. 



I =length of specimen, 

 S = section of specimen, 



d = diameter of specimen (equivalent diameter if section is square), 

 B m ean= average induction, 



jt _ /distance from centre where the induction is equal to BA 

 ~\ half-length ~~J 



a = constant in equation (9), 

 K x = „ „ „ (10). 



L. Continuity in Undulatory Theory of Condensational-rare- 

 factional Waves in Gases, Liquids, and Solids, of .Distortional 

 Waves in Solids, of Electric Waves in all Substances 

 capable of transmitting tliqjn, and of Radiant Heat, Visible 

 Light, Ultra- Violet Light. By Lord Kelvin, G.C.V.O.* 



CONSIDER the following three analogous cases : — I. 

 mechanical, II. electrical, III. electromagnetic. 



I. Imagine an ideally rigid globe of solid platinum of 

 12 centim. diameter, hung inside an ideal rigid massless 

 spherical shell of 13 centim. internal diameter, and of any 

 convenient thickness. Let this shell be hung in air or under 

 water by a very long cord, or let it be embedded in a great 

 block of glass, or rock, or other elastic solid, electrically con- 

 ductive or non-conductive, transparent or non-transparent 

 for light. 



I. (1). By proper application of force between the shell 

 and the nucleus cause the shell and nucleus to vibrate in 

 opposite directions with simple harmonic motion through 

 a relative total range of 10~ 3 of a centimetre. We 

 shall first suppose the shell to be in air. In this case, 

 because of the small density of air compared with that 

 of platinum, the relative total range will be practically that 

 of the shell, and the nucleus may be considered as almost 

 absolutely fixed. If the period is ^ of a second, frequency 

 32 according to Lord Rayleigh's designation, a humming 

 sound will be heard, certainly not excessively loud, but 

 probably amply audible to an ear within a metre or half a 

 metre of the shell. Increase the frequency to 256, and a very 



* Communicated by the Author, being the substance of a communica- 

 tion to Section A of the British Association at its recent meeting in 

 Bristol. 



