The proposition to do this originated with Dr. Weber, and acting upon this proposition a committee of the British Association, comprising nearly all the leading electricians of Great Britain, was formed some years ago, which committee, with almost perfect experimental skill, determined an absolute measure for the values of the several units required for electrical measurement. Taking as the unit quantity of electricity that amount which would be generated by a gramme weight falling through a distance of one metre in one second, the value given to the unit of resistance was such as would allow this unit quantity to flow through it in one second. The means by which the values were experimentally arrived at cannot be described here. It suffices to say, that the unit of resistance being once determined, copies of it, formed of lengths of wire of a platinum-iridium alloy, were issued, from which copies the sets of resistances now so largely employed by electricians were adjusted. Out of compliment to the great German physicist who first proposed the fundamental law which governed the flow of the electrical current, the unit of resistance was called the ‘Ohm.’ It was a marked progress on the practical application of the electric force to be enabled to measure it, and, as it were, bring it under control. Without its help the electric telegraph could not have become what it is; nor has it been without notable use in the art of protection against lightning. One of the greatest steps in advance in the application of the lightning conductor, from its discovery to the present day, has been the invention of the galvanometer. Franklin could not, but we can, test our lightning conductors. [Illustration: Fig. 1.] [Illustration: Fig. 2.]