THE 



LONDON and EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



AUG UST 1833. 



XIII. Proposed Philosophical Experiments* ByYl. F.Talbot, 

 Esq. M.P.F.R.S* 



1 . On the Velocity of Electricity. 



COME ingenious experiments have lately been made by Mr. 

 ^ Wheatstone, with a view to determine the velocity of the 

 electric spark passing through air by means of a revolving 

 mirror. But has it ever been shown with certainty that the 

 passage of electricity, even through a conducting body, is per- 

 formed in a space of time so short as to be absolutely inap- 

 preciable ? An experiment is upon record in which the spark 

 was sent through seven miles of iron wire, which it is said to 

 have traversed in an instant But it may fairly be presumed that 

 the philosophers who made this observation, could not answer 

 for an interval of time smaller than the tenth part of a second. 

 Now, as the revolving mirror gives us the power of increasing 

 the accuracy of observation at least a thousand-fold, I will 

 suggest a method of applying it to determine this question. 



Let the greatest length of wire that can be procured, be 

 disposed so that the two extremities are brought very nearly 

 together. Let one end of the wire receive the spark from the 

 machine, and the other end give it out again to any body 

 which communicates with the earth. 



If the flashes of electric light, entering the wire, and leaving 

 it after traversing its whole length, appear simultaneous to 

 the eye, take a mirror mounted on a revolving axis, and place 



* Communicated by the Author, 

 Third Series. Vol. 3. No. 1 4. Aug. 1833. M 



