MESSRS. EDITORS.Your notice in a late number ot the " Scientific American," of the Typhoductor or Storm Pointer, exhibited by Colonel Lloyd, called to my remembrance a simple contrivance, which, though not by any means new, may be so to many ot your readers, and as the experiment involved is a simple one, and easily made, it may be practically tested by all who have any doubt as to the truth of it. "Put two drachms of pure nitre and half a drachm of chloride of ammonia, reduced to powder, into two ounces of pure alcohol, and place this mixture in a glass tube, of about ten inches long and proportionate diameter, the upper extremity of which must be covered with a piece of skin or bladder, pierced with small holes. If the weather is to be fine, the solid matters remain at the bottom of the tube, and the alcohol is as transparent as usual. It rain is to fall in a short time, some of the solid particles rise and fall in the alcohol, which becomes somewhat thick and troubled. When a storm, tempest, or even a squall is about to come on, all the solid matters rise from the bottom of the tube, and form a crust on the surface of the alcohol, which appears in a state of fermentation. These appearances take place twenty-four hours before, the tempest ensues ; and the point of the horizon from which it is to blow, is indicated by the particles gathering most on the side of the tube opposite to that part whence the wind is to come." When, where, or by whom this discovery was made I do not know ; it) is simply matter of history to me ; but an old Salt, resident in Virginia, whose instrument was not the most neatly fitted, asserts, from many years' experience, that he has never known it to fail, either as a barometer or storm pointer. The rise and fall ot the sediment by atmospheric change may be readily conceived, but what subtle influence can there be which causes it to collect twenty lour hours previously, on the side opposite to that from which is the impending storm ? Are we to suppose that the particles are so nicely sensitive as to be affected by the slight difference which may exist in density of the atmosphere, on the one side of the tube over that on the other, in the transition or disturbance of equilibrium, which is being effected by the progress of the atmospheric change in the direction of, and as produced by the coming storm? Or may there be some electrical influence at work ? The causes, however, I shall not pretend to determine ; these may form a subject of enquiry for others better versed in the theory of storms than I am, but in presenting the experiment to your readers, I hope that it may not fail to interest a lew. G. January 31st, 1853.