Science Sittings

New Zealand Tablet, Volume 19, 19 July 1906, Page 35

Science Sittings

By 'Volt*

The World's Cables. There are at the present time about 225,000 miles of electric cables lying cv the bottom of the sea. About 6,000,000 messages are transmitted by cabJe every year. The working speed averages up to 100 words per minute. The average useful life of a submarine cable, under present conditions, may be anywhere from 30 to 40 ye^rs. A Great Bridge. The new railway bridge over the Yellow River in China is one of the largest and most remarkable in the world. It is a mile and seven-eights in length, and is composed entirely of steel, with no masonry whatever, according to the report of Special Consular Agent Crist. It rests on steel tubes embedded in the river bottom, and supporting a scries of arches varying from about 66 to 98 feet in length. Composition of Egg Powders. There are a number of preparations on the market known as ' egg powders.' As regards some of them, people may imagine they are using eggs, in a dried state, but apparently that is not always the case. The other day the New So-uth Wales Board of Health bad samples of two specimens examined. One of them contained wheat-flour, baking powder, ginger, and tumeric. The latter gives the mixture its yellow color. The other specimen was found to be a liquor, and to consist of nothing but a solution of an aniline dye known to the trade as acid yellow. Both of the preparations are harmless. African Grown Cotton. Sir Alfred Jones, speaMng at the annual meeting of the; African Trade Section of the Liverpool Chamber of Commerce, said tlu Cotton-growing Association were going to import into England this year between £100,000 and £120,000 worth of African-grown cotton ! In this connection he prophesied that Africa ere long would supply Lancashire with enough raw cotton to supply- her needs, and there might be some over for America. Labor, he pointed out, could be obtained in Africa for 6d a day, and land for practically nothing, which were far different conhitions from those in America. Spectacles. The oldest painting with spectacles dates from the year 1417. The picture represents the investiture of the burgrave ot Nuremberg with the margraviate of Brandenburg, and the officiating chancellor wears a kind of pince-nez ■in -green frames. but there still prevails some obscurity concerning the exact date of the invention, which is generally assumed to have occurred at tne end of the thirteen! 1 h ccntmy. Nor can we tell with certainty who the inventor was. The invention is generally asjri,bcd to two Italians, Salvino d'Armato degli Armato and Alessandro deila Spina, but the English also claim tne credit for their countryman, Rdger Bacon. Tke First Asphalt Pavement. The use of Neufchatel asphalt opposite the Custom House, Dunedm, reminds us that the first pavement of that material was laid down in Neufchatel, Switzerland. In that vicinity were the rock asphalt mines, known as the Val de Tra\ers, which were discovered in 1721 ; but it was not until 1849 the utility of asphalt as a road covering was first noticed. The rock was then being mined fo" the fhirpose of extracting the fcitumcn contained in it for its use in medicine ai !?. arts - lt is a IniK-stone found impregnated with bitumen, of which it yields on analysis, froriTß to 14 per cent. It wasi observed that pieces of rock asphalt, which fell from the waggon in transit from the imnes, were crushed by the wheels, and under the combined influence of the traffic and the heat of the sun a good road surface was produced. A macadam road of asphalt was then tr-ade, which gave very good -results ; and finally, in 1854, a portion of the Rue Bergere was laid in Paris with compressed asphalt on a concrete foundation. In 1858 a still larger sample was laid, and from that time it has been laid year after year in Paris. From Pans it extended to London, being laid in Thread n eedle street in 1869, and Uhcapside in IS7O, .and in successive years in other -streets.