42 Royal Society. 



which the radius is equal to the distance of the shorter end of the 

 propeller from the axis. The water within this circle meets with no 

 resistance until it arrives at the line joining the two extremities of 

 the propeller, when it is immediately acted upon by the eccentric 

 curved surface of the propeller. 



A paper was read, entitled, " Additional thoughts on the use of 

 the Ganglions in furnishing Electricity for the production of Animal 

 Secretions." By Sir Everard Home, Bart., F.R.S. 



The author considering animal heat as depending on the ganglions, 

 infers from the analogy of the structure of the abdominal ganglia with 

 the electrical organs of fishes, that animal heat arises from the elec- 

 tricity supplied by these ganglions. 



May 12. — A paper was read, " On a peculiar class of Acoustical 

 Figures ; and on certain forms assumed bj' groups of particles upon 

 vibrating elastic surfaces." By Michael Faraday, Esq., F.R.S., 

 M.R.I., Corresponding Member of the Royal Academy of Sciences 

 of Paris, &c. 



When elastic plates on which sand has been strewed are thrown 

 into sonorous vibrations, the grains of sand arrange themselves in 

 lines which indicate the quiescent parts of the plate, and have been 

 called the nodal lines. This fact was discovered by Chladni, who 

 also observed that the minute shavings cut by the edge of a glass 

 plate from the hairs of the violin bow employed to produce the vi- 

 bration, collected together on those parts of the plate that were 

 most violently agitated, that is, at the middle of the Hnes of oscilla- 

 tion, or portions into which the plate is divided by the nodal lines. 

 The same phaenomenon is exhibited by lycopodium, or any other 

 very light and finely divided powder. This subject was investi- 

 gated by M. Savart, who, in a paper read to the Royal Academy of 

 Sciences at Paris in the year 1817, endeavoured to account for this 

 latter class of phenomena by deducing from the primary divisions 

 of the parts of vibrating bodies, certain secondary modes of divi- 

 sion, comprising parts that remain horizontal during every stage of 

 the vibration, and which therefore may admit of the settlement there 

 of light powders, while heavier powders can be stationary only at 

 the points of absolute rest. 



This explanation not appearing to the author to be satisfactory, 

 he made a great number of experiments, which are detailed at length 

 in the present paper, showing that the immediate cause of these 

 motions exists in the surrounding medium, and is to be found in 

 the currents arising from the mechanical action of the plate, while 

 vibrating upon that portion of the medium which is in contact with 

 the plate. These currents* are directed from the quiescent lines 

 towards those parts where the oscillation is the greatest, and meet- 

 ing from opposite sides at these central points, thence proceed 

 perpendicularly from the vibrating surface to a certain distance ; 

 and finally, receding from each other, return again in a direction 

 towards the nodal lines. The combination of these motions consti- 

 tutes vortices carrying with them any light particles which may lie 

 in the way of the currents. While in motion, the powders sustained 

 by these vortices appear in the form of clouds, the particles of which 



have 



