OF ELECTRICITY AND THE DURATION OF ELECTRIC LIGHT. 591 



I have also proposed various modifications of parts of the instrument, § 4, to suit 

 particular experiments, and to ensure additional accuracy in the repetition of those 

 already made ; but not having yet put these to the test of experiment, it would be 

 premature at present to describe them. 



The instantaneousness of the light of electricity of high tension, rendered evident 

 by the preceding investigations, affords the means of observing rapidly changing 

 phenomena during a single instant of their continued action, and of making a 

 variety of experiments relating to the motions of bodies when their successive posi- 

 tions follow each other too quickly to be seen under ordinary circumstances. 



A few obvious instances will at present suffice. A rapidly moving wheel, or a re- 

 volving disc on which any object is painted, seems perfectly stationary when illu- 

 minated by the explosion of a charged jar. Insects on the wing appear, by the same 

 means, fixed in the air. Vibrating strings are seen at rest in their deflected positions. 

 A rapid succession of drops of water, appearing to the eye a continuous stream, is 

 seen to be what it really is, not what it ordinarily appears to be, &c. 



§7. 



The preceding experiments having been directed rather to detect elongations and 

 deviations than to measure them, I am not prepared to state the results with numeri- 

 cal accuracy. I shall endeavour to supply this deficiency in further investigations, 

 but must at present content myself with stating the following general conclusions, 

 deduced from the appearances which I have observed, though, I must allow, more 

 accurately performed experiments are required before they can be considered as fully 

 established. 1st, The velocity of electricity through a copper wire exceeds that of 

 light through the planetary space. 2ndly, The disturbance of electric equilibrium in 

 a wire communicating at its extremities with the two coatings of a charged jar, travels 

 with equal velocity from the two ends of the wire, and occurs latest in the middle of 

 the circuit. - 3rdly, The light of electricity in a state of high tension has a less dura- 

 tion than the millionth part of a second. 4thly, The eye is capable of perceiving 

 objects distinctly, which are presented to it during the same small interval of time. 



By prosecuting these researches with instruments of higher power, and of greater 

 accuracy in their indications, numerical laws may be established for a large class of 

 phenomena, the relations of which we have had hitherto no means of observing. The 

 relative velocities of electricity in different metallic wires ; the modifications in the 

 velocity of electricity in different states of tension when passing through the same 

 conductor, if any such differences exist ; the duration of the electric spark under 

 diflferent circumstances of tension and quantity, &c., will be among these objects of 

 investigation. 



4 G 2 



