fully of the possibility of distributing the electric light from house to house; but to-day the problem does not present any greater practical difficulty than the distribution of water or gas. When Sir Humphry Davy first made an exhibition of the arc light he used for the purpose a battery of two thousand voltaic cells. Light so produced could never have come into general use on account of the excessive cost. Faraday had to formulate the laws of induction, and the dynamo had to be developed, before Davy's discovery could be turned to practical account, and even then a vast amount of ingenuity had to be expended in the arrangement of details. The incandescent light was a later development. An incandescent lamp is a simple thing to look at, but only those who have studied the subject know how much of laborious experiment and research it took to bring it to its present condition of perfection. The dynamo which, practically speaking, gives us the electric light, gives us also electric traction and electric power generally. We are only beginning to realize the advantages which our newfound force may have in store for us in this direction. Every month the electric street car is more and more displacing the horse car, with added comfort to passengers and diminished wear of our thoroughfares. Power is conveyed silently over wires from central stations and distributed wherever it may be required for manufacturing purposes, saving a vast outlay in separate boilers and engines, and greatly economizing space. In great telegraph centers the dynamo is displacing cell batteries for the production of current. It is also used for electrolytic operations on a large scale. Nothing, perhaps, is more impressive than to witness the operation at the same moment and on the same spot of three distinct forms of force, mechanical or physical, electrical and chemical, one merging into the other. The waterwheel or the steam-engine furnishes mechanical power; the dynamo, taking up that power, converts it into electrical energy, which again, conducted to an electrolytic cell, is further changed into chemical action. Nothing could more powerfully bring home the lesson that, in the last analysis, all energy is one. Vast industries would disappear from the earth if the various applications of electrolysis could by any means be lost—electro-plating, electrotyping, electrometallurgy, and a hundred other special applications of electro-chemistry. It takes a considerable effort of thought and memory to realize the extent to the every-day operations of the modern world are dependent upon a power which but a few generations ago was a matter of more or less crude speculation and idle wonder. In electro-welding we have a process, strictly speaking, analogous to the production of the electric light; the energy of electricity is converted into heat at a given point with the most marvelous results. The new science is stretching forth its hands in every direction, and its achievements to-day are but an earnest of what it is destined to accomplish in the near future.
There is, however, another aspect of the matter which is deserving of attention. From having been, up to a short time ago, a subject concerning which the most vague and confused ideas were generally entertained, electricity is now furnishing matter for the formation of one of the most exact sciences. It is true there is a vast amount of popular ignorance respecting it still; one might not, perhaps, have far to go to find "educated" people who imagine that Edison and electricity are almost convertible terms, or at least that electricity was fished bodily out of the depths of the unknown by Edison; nevertheless, the light is spreading, and the very operations which the applications of electricity involve are furnishing a valuable education to a large section of the community. Electricity is above all things measurable, and measurable in a great variety of ways; and the measurement