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XIII. The Bakerian Lecture. — An Account of several new Instruments and Processes 
for determining the Constants of a Voltaic Circuit. By Charles Wheatstone, 
Esq., F.R.S., Professor of Experimental Philosophy in King's College, London, 
Corresponding Member of the Academy of Sciences at Paris, fyc. 
Received June 15, — Read June 15, 1843. 
§ 1 . 
X INTEND in the present communication to give an account of various instruments 
and processes which I have devised and employed during - several years past for the 
purpose of investigating - the laws of electric currents. The practical object to which 
my attention has been principally directed, and for which these instruments were 
originally constructed, was to ascertain the most advantageous conditions for the 
production of electric effects through circuits of great extent, in order to determine 
the practicability of communicating signals by means of electric currents to more 
considerable distances than had hitherto been attempted. In this endeavour, guided 
by the theory of Ohm and assisted by the instruments I am about to describe, I have 
completely succeeded. But the use of the new instruments is not limited to this 
especial object ; they will, I trust, be found of great assistance in all inquiries relating 
to the laws of electric currents, and to the various and daily increasing practical 
applications of this wonderful agent. An energetic source of light, of heat, of 
chemical action and of mechanical power, we only require to know the conditions 
under which its various effects may be most economically and energetically manifested, 
to enable us to determine whether the high expectations formed in many quarters of 
some of these applications are founded on reasonable hope, or on fallacious conjecture. 
The theory we now possess is amply sufficient to direct us rightly in this inquiry, but 
experiments have not yet been sufficiently multiplied to enable us to obtain, except 
in a few cases, the numerical values of the constants which enter into various voltaic 
circuits ; and without this knowledge we can arrive at no accurate conclusions. 
§ 2 . 
The instruments and processes I am about to describe being all founded on the 
principles established by Ohm in his theory of the voltaic circuit, and this beautiful 
and comprehensive theory being not yet generally understood and admitted, even by 
many persons engaged in original research, I could scarcely hope to make my de- 
scriptions and explanations understood without prefacing them with a short account 
