Messrs. Editors—Among the physical sciences there is, perhaps, none more interesting to all classes than electricity. The reasons are obvious ; it admits of ocular demonstrations of the most pleasing character. Electricity, like light and heat, is one of the imponderables—we know nothing of it except in connection with matter. There is a hypothesis that meets with much favor with many able philosophers, viz., that there is an etherial agent pervading space, and when acting on matter in one form produces light, in another form heat, in another, electricity. The imponderables, in many respects, are analagous. Light is composed of undulations, of which there are 52,000 in a single inch, and it moves 192,000 miles per second. Electricity also moves in a wave, or undula-tory form, and travels 57G,000 miles in a second. By the single fluid theory (which to me appears the most rational) Dr. Franklin succeeded in accounting for all the electrical phenomena. The two conditions he termed "plus" and "minus;" yet the theory of two fluids is quite universally adopted, and is much the most convenient. If the nerve connected with the stomach of any living animal be separated, and the poles of a galvanic battery applied to the stomach, digestion goes on as perfectly as before separation; and yet it has been clearly shown that the nervous force is not electricity. Again, if the poles of a powerful battery be applied to the nerves of a human subject soon after life is extinct, all the phenomena of life are produced in the most marked degree, such as the raising and depressing the chest, as in powerful breathing, opening and closing the eyes and mouth, appearances of mirth and anger, and even pointing the finger and shaking the fist. Some experiments of this kind have been of such an extraordinary character that many present have been induced to believe that life had actually returned, and that the subject was about to take vengeance on all in the room. This is one form in which - this mysterious agent is made to manifest itself. In another form wc see it entering the workshop, a humble companion and faithful servant; diligently searching the liquid solution for minute particles of silver, and carefully depositing them in a metallic form, according to whatever pattern is presented to it. One electric battery will perform the work of about twenty men by the old way, and it will be infinitely more perfect. In still another form it becomes our faithful messenger, conveying glad tidings to distant friends; or the mournful intelligence of departed relatives. It travels on a slender thread of wire beneath the ocean depths, or over the mountain steeps, through wind and storm, the gloomy forest, or darkest night, and it delivers with truthfulness whatever message is intrusted to its care. In another form we behold this wonderful agent taking up a permanent residence in the delicate points of the mariner's compass, and pointing, with unerring certainty, the course to be taken over unknown waters, thus enabling man to make the trackless ocean a highway. By this simple form of electricity the destiny of empires have been controlled. Where would America, with all her greatness, have been to-day, or what would the commerce of the world be, without electricity in the mariner's compass ? Let those opposed to improvements and developments of genius answer. Another useful application of this agent is the blasting of rocks in our harbors, and the throwing down of stupendous cliffs, to make a track for the locomotive. Many feats have been performed in blasting that would have been impossible without the aid of electricity. Many attempts have been made to use it as a motive power, but the result has not been very successful. In all cases it has been found to be more expensive than steam ; yet the results have perhaps been as encoura, ging as in the early attempts to use steam. ^ Here is a wide field for inventors. The application of the lightning rod was a 1^great achievement in conducting this subtle I iluid harmlessly from ourdwellmgs and ships. The loss to the British navy was enormous previous to the successful application of the lightning conductor by Sir Wm. Snow Harris, since which I believe not a vessel has been lost by lightning. Electricity is the most subtle and powerful agent in nature. We behold the sturdy oak, the pride of the forest, whose strong arms have withstood the rude winds for centuries, bow in an instant to a single stroke of this mysterious agent. The most refractory substances in nature, which refuse to yield to the strong blast of the furnace, are instantaneously deflagrated by this agent. We behold it in the beautiful coruscations of the aurora bore-alis ; it forms the nucleus of the terrible tornado ; it is heard in the thunder, and felt in the earthquake. I have thus very briefly noticed some of the phenomenon of this wonderful agent; and although it has been applied to many useful purposes, it would be ridiculous to suppose that all its useful applications have already been developed. To my fellow-mechanics let me say, bear in mind that the Deity thundered over the heads of men for about six thousand years, to arouse their intellect, before a Franklin and a Morse responded to the call of the Great Infinite. Young America may well be proud of the names of these philosophers and inventors; but while we have made such progress in the arts and sciences, we should never be unmindful of the duty we owe to the great Creator of these powers of nature, who has given them to man as wonderful agents, to be employed for his good. L. A. Orcott. Albany, N. Y., June, 1858.