We take the following from the London Photographic News: A novel application of the stereoscope was announced a year or two ago by Professor Dove. It consists in the detection of reprinted matter in the case of books, pamphlats, &c., and was based upon the impossibility, or at least extreme difficulty, of compositors, when setting up a page of type w i th t he i n tent ion of prod ucing a fac-simile of a page of printed copy, making the blank spaces between the separate words in a line, exactly the same width in the copy as in the original. Our rcaders may not all be aware that the blank spaces between the words w 1iich they are now looking at are made by placing very thin strips of lead or type metal, technically called " spaces," side by side between each group of types forming a word, an d so arranging them as to obtain each line of the projjei length. These lead " spaces" arc so thin that in ordinary work it is never attempted to get exactly the same number between each word, but they are put in in more or less numbers, according to the way in which tht words fall at the end of a lineif the line as it is set uj in type fiills a trifle short of the proper length, it is " spaced out ;" and if it exceeds that length by a lettei or two, some of the "spaces" are removed, or thinnei ones used. In tinS mann er it will be perceived that however accurately the compositor follows the words of his prin ted copy, and se ts up his page in imitation of the original, he is sure to be sometimes incorrect with the spacings between the word s. A kno wledge of these facts led Professor Dove to i magi ne that if a stereoscopic slide were so mounted as to have the originai printed page o n one s id e, and the recomposed fac-simile on the other half, an i n spec tion in the instrument would at once detect the repri nt. And so it was seen to be on trial. The page of print which the eye apparently saw formed by the superposition of the two stereoscopic cor-pul prese n ted the remarkable appearance of not being on the same flat surface, nearly every alternate word started up or retreated to a different plane from its neighbor and the whole effect was most strange and disjointed as if the observer were looking at three or four superposed sheets of glass, with the words forming the page dotted at random on different sides ot the glass plates. We have thought it right to enter Into this at some length, inasmuch as though it was mentioned in some scientific works when first discovered, it was never brought very prominent'ly before the readers ot the Photographie News, and also because a knowledge of the foregoing facts is necessary to a proper understanding of what the learned professor has recently discovered. It has been found that wires of different metals, Q i.i'.-.n through the same plate, are not all of the same thickne^, for they are of diff'erent degrees of elasticity, and .niter being drawn through the plate they expand to differem ainounts. This exi'uijoioii is l'roved by the fact that with the exception of gold no wire can be drawn th rough the same aperture through which i t has been pressed. Silver requires the least force, but the expansion caused by elasticity continues for several weeks. It appeared probable to Professor Dove that in stamping metals something similar would take place, and that medals of different metals, stamped in the same die, would be of different sizes. This would be most readily seen in those medals in which the impression is symmetrically arranged in reference to the edl!e, as is the ease with the medals of tlie French Exhibition, in which the coat of arms encircle the French eagle in the middle. One of these i n silver and one in bronze were placed in thtl stereoscope, the eagle being fixed in the middle. After some time the stereoscopic combined medals were seen i n the form of a hollow escutcheon, and of the color of an alloy of the two metals. Evidently the reason of this lies in the nonius-like shifting of the individual lines of the impression. This same result was also obtained by the professor with large gold and silver medals, which were kind ly entrusted to him by the roy al mint in Berlin. It was probable that medals obtained by casting would show the same thing, an d this was found to be the case with tin, bismuth, and lead, the casts in wh ich were be autifully executed by Professor Kiss. The account from which the above is derind appeared in Poggendorff"s Annalen, and also in the Pii/osqphical ^klagazine for the present month. Himo's crown led to the use of specific gravity to detect an adulteration. The stereoscope is a new means. value OP NEWSPAPERS.One thousand pounds sterling has recently been offered in London for a complete set of the Times newspaper for a public library at Melbourne, Australia, but without success. The fact is an instance of the rising importance of the things that, at the moment, seem only of trivial valuc scarcely worth preservingbut which, to succeeding generations, afford the most authentic sources of knowledge concerning the " form and pressure" of their time. The British Museum now collects and presenes everything ; and the Bodleian Library, which was expressly debarred by its founder from admitting the vain and trivial light literature of the date of its formation, is now glad to purchase the sixpenny and shilling plays and pamphlets of that day at prices from 50 to 150 each. AN important series of experiments connected with electric telegraphy have recently been communicated by Dr. Mathiessen to the Royal Society. He has been induced te investigate the influence which an admixture of foreign bodies has upon the electric conducting power of pure copper, by reason of the great discrepancies which different samples of copper wire presented, w h en tested for electric telegraphic purposes as to their pow er of conductin g the electri c current; some speci-mens of apparently equal purity having less than half t he conducting value of others. In the outset of his experiments the doctor found that one great source of the discrepancies hitherto noticed has been the presence of oxygen, which, it is well known to smelters, copper ?absorbs With avidity. This element, when present in very small quantity only in the copper wire, reduced its conducting power from about 93 to about 70. The effect of carbon, sulphur, phosphorus, seienium, tellurium and arsenic were like wise tried, and in each instance the presence o: the metalloid was found to have a strongly marked prejudicial effect on the conductmg power, in some cases (with phosphorus and arsenic) sinking down from 93 to between 6 and 7. The effects of different pure metals, such a.s zinc, i^^n, tin, silver, gold and lend, were next tried, but with one uniform result, namely, that of deteriorating the conductibility, and Dr. Mathiessen has hence been led to this important conclusion, that "there is no alloy (!If copper which conducts electricity better than pure copper." THE Great Salt Lake lies at an elevation of 4,200 feet above the level of the sea, and is seventy miles long. When its waters evaporate, they leave a deposit of about two ches thick, of sa^e m^er. MANUFACTURES IN MANCHESTER, N. H. Manchester, N. H., built at the Amoskeag Falls, in the Merrimac river, is one of the cities of New England which have had a marvellous growth, rising from feebleness and insignificance to places of great business and industrial importance in a few years. I n 1840, Manchester had a population of 3,223; in 1850, 13,932 ; in 1854, 19,897, and in 1860, about 25,000. Its grow th began in 1838, at which time there were, within the limits of the city proper, not more than fifty inhabitants. We have before us a chart of the statistics of Manchester manufactures for 1860, from which we learn that the capi t al stock of t he m anufa c t uri ng c om p anie s is $ 6, -840,000, which run 6,154 looms and 229,132 spi ndl es. Number of female operatives, 4,890; male operatives, 2,490 ; con s um ptio n of cotton per week, 385,000 lbs.; of w ool, 30,000 lbs.; yards m ad e per w eek, 1,133,500; yards printed per annum, 17,500,000; 2,300,000 seam -less bags per annum are woven here. The monthly pay roll is $139,200. Besides the mann fac ture of fabrics, steam fire engines, locomotives, and all kinds of mill machinery are made here; all kinds of axes, ad zes, h atchets, &c., book a nd newspape r, c ast ings, &c. Notwithstanding the large number of mills already in operat i on, it is said that not m ore than half the water power of Manchester has been brought into requisition, and that some operations will be developed ere long which will greatly increase the population of the city. World. EXAMINATION OF INVENTIONS AT THE PATENT OFFICE.Through the Branch Office of the SCIENTIFIC AMERICAN, located directly opposite the Patent Office, Washington, D. C., we are enabled to make special examiniitions into the novelty and patentability of inventions. By having the records of the Patent Office to search, and the models and drawings deposited therein to examine, we are enabled to give an inventor advice, not o nl y as to the: probabilities of his obtaining a paten t, but also as to the extent of the claim thit it is ex ped ient to s e t up w hen the papers for an app l icati on for a pa ten t are prepared. For a special examination at the Patent Office, we make a charge of Five Dollars. It is necessary that a model or drawing, and a description of the invention shall accompany the remittance. Address MuNN & Co., No. 37 Park-row, New York. IN a recent report of the directors of the Great Eastern, it is stated that the screw shaft had worn itself down in the bearings to an extent of 4 inches. There were patches on the bottom from which the paint had been worn and these had rusted to the depth of 1-32 of an inch. Not a single rivet, however, was moved in the least. THOUGH the surface of mother of pearl seems perfectly smooth to the touch, its reflection of prismatic colors is proved to be owing to exceedingly minute inequalities in its surface, shown by taking an impression from it in black wax, when the wax is found to reflect the same colors. HERODOTUS, the father of history, tells of a building connected with the temple of Latona, at Buto, the walls of which were formed of a single rock 58.8 feet long, and as many in hight and depth. The covering or roof of this h ou s e was also a si ngl e block 5.28 feet in thicknoss. The interior was hollowed out of the s ol i d rock. WHY do printers not succeed to the same extent as brewers? Because printers work for the head and brewers for the stomach ; and where twenty men have stomachs but one has brains. Some pieces of hemp rope fished up from the wreck of the Royal George, at Spithead, have been found perfectly sound after being about a century under water. The smell of tar upoT! them was qnite fresh. OBJECTS under water, to an eye in the air, appear larger than they are ; and to fishes under water, objects in the air appear less than they are. A street railway is about to be laid down in Manchester, upon the American system- as introduced into England by Mr. Train.
This article was originally published with the title "Practical Value of the Stereoscope"