This improvement is liascd npon the truth that it is not enough that wo get air to breathe, we must have ptm air it we expect to retain health or recover from disease. The device not only admits air, but it filters and absorbs. The air in entering through it passes through a layer of sponge which filters out floating organic dust, and absorbs extraneous moisture. It next passes through a layer of charcoal lumps, which absorbs any foul gases present in it, and finally enters the room through a finely perforated screen which prevents the formation of sharp currents, and gently diifuses it, directing it inward and upward. Its operation will be seen upon reference to the engravings. Fig. 1 is a view of the ventilator as seen from the interior of an apartment. Fig. 2 is an exterior view of it placed in a window, and Fig. 3 is a sectional view exhibiting its construction, which is extremely simple. A is the layer of sponge resting upon a finely perl'oratod plate of sheet metal, B is a layer of lumps of charcoal, the powerfully absorbent quality of which is well known, resting on a second perforated plate, having slats, cross sections of which are shown, immediately over it, so as to keep an open space between the layer of charcoal and the perforated dome through which the air finally flows. This ventilator is constructed upon sound scientific principles, and the employment of well known and thoroughly proved means to accomplish the ends sought, will give confidence to their tasteful combination, as used in the apparatus. It was exhibited to the New York Association for the Encouragement of Science and Arts, and a committee was appointed to investigate its merits, which made a very favorable report. The following extract from this report suSiciontly sets forth the views of this committee. " Your Committee, after careful examination and mature deliberation are convinced that the Lesperance ventilator will perform all that the inventor proposes it should do, and we hail with great satisfaction this addition to science and art, considering that it will be found one of the best means for the preservation of health, and its restoration to diseased bodies, especially in hospitals." It is also heartily indorsed by Professor Henry, of the Smithsonian Institute, and other leading scientific men. It was also exhibited before the Polytechnic' Association of the American Institute, April 15, and the minutes of the meeting show that it was considered by the members present as a very important and valuable improvement. The instrument has been placed upon many public buildings, hospitals, etc., and receives from all who have used it the highest testimony in its favor. Among the most valuable of these is one from Henry Howard, M. D., formerly surgeon of St. Patrick's Hospital, Montreal, now Professor in the St. Lawrence School of Medicine. This gentleman states that while in charge of the Provincial Lunatic Asylum the building was crowded with patients to the extent of twice as many as hygienic principles would justify, and although he made the utmost exertions to properly ventilate the building, using for that purpose all the usual appliances, everything failed until Lesperance's ventilator was tried. The latter was placed in every window of the asylum, and found to completely ventilate the building. He adds that he has tested the ventilator in every possible way known to science, and found it perfect. It will be seen that the air enters this ventilator by virtue of the pressure of the external air, the specific gravity of the air inside an occupied and warmed room being less than that outside. Hence it is not subject to being aflected by external winds as much as many other kinds cf apparatus. It appears to us to be one of the most important devices yet invented to secure ample and perfect ventilation in public school buildings, hospitals, churches, and private dwellings. This invention was patented through the Scientific American Patent Agency, February 9, 1869. Address for further information Thomas Howard, P. 0. Box 3,088, New York City. " Galvanized Iron." Three centuries ago, says Engineering, a French monk wrote of the injurious efl'ects attendant upon the use of copper cooking utensils, and he also attributed like eifects to the use of iron vessels. He proposed to coat the interiors of the vessels, in both instances, with zinc, and that by almost the identical means now followed in the so-called galvanized iron manufacture. The term " galvanizing," long known to be incorrect, was introduced, we believe, by Mr. Malins, a brother of Vice-Chancellor Malins, and it was the same gentleman who promoted the formation of the Galvanized Iron Company, long known as the firm of Tupper and Carr, the senior partner of this firm being, by the way, no other than the eminent " proverbial philosopher." Messrs. Morewood and Co., of Birmingham, have long been among the largest manufacturers of galvanized iron, employing, when in full work, about 450 men and boys at their plate mills at Bilston, and 250 at their galvanizing works at Birmingham heath, where as many as 180 tuns of plates have been turned out weekly. The processes of tinning and " galvanizing," i.e., zincing, the plates, or other objects, has often been described, and the greater proportion of galvanized goods being merely zinced, the operation is one, mainly, of removing the scale by sulphuric acid and afterwards immersing the articles in a bath of melted zinc. The " continuous roofing sheets," formed by gripping and rolling together the edges of galvanized plates, end to end, to lengths up to 500 ft. where required, have come into extensive use. These, and all galvanized plates are known to stand well where unaffected by sulphurous fumes as from coal, and even where a good deal of coal is burnt beneath a galvanized roof it is nearly certain that the zinced plates last longer than plain iron, however painted. Hoofs of the great spans now made, sometimes upwards of 200 ft., could not well be slated, and pure zinc, by its great expansion and contraction, is objectionable where tho extremes of temperature are considerable. Artiflcial Ice Manufacture. The Evening Tclcrjram says that the ice factory at New Orleans, situated in one of the elevators, is a great success. It consists of six retorts of a chemical freezing mixture. From these six retorts six pipes descend to six huge chests, which chests in turn radiate severally off into four compartments. In each compartment are long, thin, tin cases, seven on one side and seven on the other. This making by all the rules of arithmetic a total of fifty-six cases in a box, and their being four boxes to a chest, and six chests to a factory, it follows that at full blast this Southern ice factory can turn out 1,344 cakes of ice, eighteen inches long, twelve broad, and two thick, at the completion of each process, The ice is much harder than that frozen naturally, and lasts much longer. The factory is a joint stock enterprise, and the property is exceedingly lucrative.