SCIENTIFIC.

Otago Witness, Issue 1866, 26 August 1887, Page 36

SCIENTIFIC.

Everybody who has used the Brooklyn bridge must have noticed the overlapping elides at the middle of each span that allow the structure to grow short or long, as thte weather grows cold or hot* and the marks thereon that indicate a distance of several feet between the extremes of contraction arid expansion. Yet few suspect that the bridge contracts or expands sideways from heat o£ the sun* though the degree is so small as to be almost imperceptible, and not nearly so great as if the bridge ran north and south. The same phenomenon has been noticed of late in structures of stone and iron. The Washington monument leans to the east in tke morning and to the west in the afternoon. A plummet line suspended in the interior of the dome of the capitol at Washington was found by actual measurement to Bwing overa space of 4£in, making a total dip from the perpendicular of B^in. This movement involves the entire dome. ' A learned monk some years ago suspended a plummet in this way from the top of the dome of St. Peter's at Rome, and was astonished to find this mysterious movement. He attributed it to a third and undiscovered motion of the earth, but it was afterwards explained as the effect of the action of the sun on the metal of the dome.

At a recent meeting of the Association of Public Sanitary Inspectors Dr Alfred Carpenter made some remarks on the " Theory and Practice of Disinfection," which, we trust, will serve to dispel many erroneous notions concerning that important operation. He said that the breath of a smallpox patient contains the germs of living protoplasm, which would take root if immediately transplanted to the membrane of a susceptible person ; but if floated about in the air for a hundred yards ; such germs will loose their vitality. Here we recognise the importance of isolation of the patient in such cases. He advocates the use of steam for disinfecting houses, in preference to carbolic acid, which tends to preserve the dormant germ from decay. The same remark holds good for alcohol ; so that those who think that they render suspected water innocuous by mixing with it something stronger, are under a delusion. The best of all disinfectants is bichloride of mercury (corrosive sublimate) ; and, according to Dr Carpenter, a solution of one part in five thousand parts of water will in a quarter of an hour destroy every living germ, dormant or otherwise, with which it comes in contact. One ounce of the corrosive sublimate would afford a solution of this strength when mixed with thirty- one gallons of water, the cost being about sixpence. It should be mentioned that the greatest caution must be exercised in dealing with this salt of mercury, for it is one of the most virulent poisons known to chemists.

Iron, says : " Our American contemporaries have every cause to be surprised at the astonishing fact that thousands of tons of scrap iron are every year taken to the United States, and there converted into the simplest of American manufacturers — the sad or laundry-iron — and then exported back to Europe at no small profit. There is not one corner of Europe where American small cast hardware is not on sale. The toolmakers and machinists of Europe — such as Krupp, of Germany, Whitworth and Armstrong, of England, and Hotchkiss, of France, with their vast resources — are unable to produce a Moncky or. screw-bar wrench equal to the American wrenches, and consequently they have to import these tools from the States. It is stated that there are no less than 80,000 dozen of them exported to Europe alone every year. It is interesting to note that Charles Moncky, the inventor of this screw-bar wrench, received only 2000dol for his patent, and is now living at Williamsburg, Brooklyn, in a small cottage bought from the proceeds of this sale. In the matter of the common pocket wood-box rules, also, the American manufacturers so far excel all others that, if not all European nations, certainly all nations outside of Europe, are supplied from America. The manufacturers there print on the rule whatever system of measurement is followed by the country for which the goods are intended. American augers and auger-bits are used the world over, no other nation being able to compete. The Americans, with such facts before them, may well be proud of their manufacturers."

The application of photography to land surveying has made great strides of late years, chiefly in the hands of French engineers. By the most recent system a fairly accurate survey of a wide extent of country can be obtained by the taking of six photographs at each of two stations at the ends of a measured line. By the construction of simple diagrams the position and level of any points visible in the photographs can be determined, and ordinary maps and contour maps of the country can be prepared.