Elements of electricity, magnetism, and electro-magnetism : embracing the late discoveries and improvements : digested into the form of a treatise, being the second part of a course of natural philosophy : compiled for the use of the students of the University at Cambridge, New England / by John Farrar.

  • Farrar, John, 1779-1853.
Date:
1826
Catalogue details

Licence: Public Domain Mark

Credit: Elements of electricity, magnetism, and electro-magnetism : embracing the late discoveries and improvements : digested into the form of a treatise, being the second part of a course of natural philosophy : compiled for the use of the students of the University at Cambridge, New England / by John Farrar. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    unequal quantities of electricitj. Indeed, whatever be tlie mag- nitude of tiie fixed ball compared with the moveable one, and whatever be the quantity of electricity at first given to them, whether they are electrified simultaneously, or one after the other, and in whatever proportion, the momentary decrease of their whole repulsive force, measured at the same distance, is al- ways in the same proportion to its intensity; and thus our ex- periments are all equally suited to the purpose of finding this common ratio. Moreover, this ratio is still the same when we employ balls of different substances. The nature of the substance has absolutely no influence on the loss of electricity occasioned by the contact of the air, at least with respect to the portion which acts at a distance by attraction and repulsion ; and this confirms the observation which we have before made, that mate- rial bodies do not seem to retain the electric principle by any proper affinity, but by the effect simply of the resistance which is opposed to it by the surrounding air. For example, in weath- er when the electricity was decreasing at the rate of -g\ a minute for each of the pith balls of the balance, Coulomb found that it decreased also j\ when he substituted for one of these balls a ball of copper; and, which will appear still more extraordinary, the decrease was also j\ for a ball of sealing wax, which had been charged with electricity, by bringing it in contact with a body strongly electrified; and thus the surface of such a body opposes no difficulty, to the transmission of the electric principle, and has no influence in retaining the portion of this principle, which manifests itself by its reaction, when once it becomes free. 23. We have as yet considered only bodies of a globular shape; but whatever may be the figure of the electrified body, whatever its magnitude and the distribution of its repulsive force, if the air is very dry and the electricity communicated not very intense, the momentary decrease of the repulsive force is always the same, and preserves always the same ratio to its intensity. This was demonstrated by Coulomb with a globe of a foot in diameter, and with cylinders of all diameters and all lengths. He substituted for the balls of his balance, circles of paper or metal; he also, in one instance, armed one of them with a cop- per wire I of an inch in length, and ^V in diameter; and he