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LIX. Remarks on the Dynamical Theory of Electricity. 

 By C. Brooke, M.A., F.R.S. 



To the Editors of the Philosophical Magazine and Journal. 



Fitzroy Square, W. 

 Gentlemen, Nov. 10, 1866. 



SINCE I sent to you, through Professor Tyndall, a short 

 notice of a fact in thermo-electricity, I have had under 

 revision my chapter on organic electricity, and have been for- 

 cibly impressed by the harmony existing between obvious de- 

 ductions from the dynamical theory and some recently observed 

 physiological results. 



The physiological effects of acting causes incidental to the 

 transmission of a continuous voltaic current through a musculo- 

 motor nerve are of a complex character; they are universally 

 acknowledged to be manifested only at the moments of closing 

 and opening the circuit, but are modified by the influence of the 

 current, during its prolonged continuous passage, on the por- 

 tion of nerve-tissue included in the circuit. 



In order to interpret correctly all the observed physiological 

 effects, it becomes necessary to consider carefully the dynamical 

 consequences of the passage of a continuous succession of elec- 

 tric waves, here assumed to constitute a voltaic current ; and it 

 will appear that the physiological results are remarkably in ac- 

 cordance with the dynamical theory of electricity. The passage 

 of a voltaic current, then, must comprise three distinct phases : 

 first, the momentary passage of the molecules of the conductor 

 from a state of rest to a state of motion ; secondly, the indefinite 

 continuance of molecular motion ; and thirdly, the return of 

 the moving molecules to a state of rest. 



The first phase will be accompanied by a rush, or sudden 

 impulse of increased potential in the direction of the current, 

 because there must be a condensation or accumulation of motion, 

 in consequence of the inertia of the molecules at rest opposing 

 the transmission of the wave : this may be termed the initial 

 current. During the second phase there will be (supposing the 

 potential of the current to remain constant for the time) con- 

 tinuous and uniform wave-motion. During the third phase, the 

 excitation of motion ceasing, the vis viva of the moving particles 

 will accumulate motion towards the termination of the conductor, 

 whence a reflex motion may be expected to be propagated (as in 

 the case of a wave travelling from the hand along a stretched 

 cord, which reaching the fixed end, is reflected back again), 

 giving rise to a momentary terminal current, inferior in intensity, 

 and opposite in direction to the initial current. 



These initial and terminal currents (or impulses, as they might 

 Phil. Mag. S. 4. Vol. 32. No. 218. Dec. 1866. 2 F 



