SCIENTIFIC.

Otago Witness, Issue 1967, 5 November 1891, Page 45

SCIENTIFIC.

-'-Most people, it may be supposed, are quite satisfied that the earth is round, from the various methods of proving it already known. A new proof has, however, been added to the number, and an account of it is , given in the current number of L'Astronomie. Observations made at Catania in 1886 by M. Ricco show that the mirage of the sun reflected in the sea is suoh as would be reflected by a convex mirror.

— An immense improvement has recently been effected in the manufacture of glass for optical instruments by means of the addition, to the ordinary materials, of phosphorus and chlorine, which, in/ some unexplained way, cause the glass to be very much more transparent, and enable it to receive a much higher degree of polish than any optical glass hitherto manufactured. Thus microscopes can be made which will render objeotß visible which are only of the diameter of oneeight millionth part of a millimetre, whereas with the best instruments now in use the diameter of the smallest object that can be seen is one-sixteen thousandth of a millimetre. A millimetre is the one thousandth part of a yard, its decimal portion of a yard being thus represented, 0001. Writing some years ago Dr. W. B. Carpenter states that the researches of Professor Abbe have shown that by microscopic power lines or marks could be distinguished or seen as separate objeots if they were only the width of the 146,528 th part of an inch, but he considers the limit of visual resolution depending on the power of the eye to be about the one hundred and eighteenth of an inch.

— A curious new use has been found for leeches. They have a faculty of storing away blood they suck for future use, and though undigested it, does not go bad on their hands. A bacteriologist has had the happy thought to use the leech for the extraction of blood supposed to contain bacteria, and for its preservation for future study. In this way he has kept the bacteria of relapsing fever alive for a long time outside the patient's body.

— Tin plate is made by coating sheets of iron with a layer of tin. The best kind is known as blook tin, being that which is covered with the thiokest layer of tin and afterwards hammered upon a polished anvil, in order to consolidate the coating and make it adhere more firmly. On being exposed to the action of the air, pure tin is not affected at ordinary temperatures. As soon, however, as a portion of the tin is removed by injury so as to expose even a tiny speck of iron surface, corrosion at once sets ' in and proceeds very "rapidly. The reason of this is of an electric nature. Iron and tin together form what is called a "galvanic couple," which will decompose the water (charged with * carbonic acid) deposited upon them from the air. Oxygen and hydrogen gases are liberated, and the iron, havjtog the greater affinity for/the 'oxygen) is.the metal attacked. Buoh corrosion is very rapid when the exposed iron surface • cbmes' in contact with water highly oharged-with carbonic acid in a mineral water factory. Mr John Aitken has modified his dustcounter'and adapted it for s counting the number of water- partioles in a fog. Fog, mist, and rain are in reality different phases of the same phenomenon .' Abundance of dry dust ,partioles in the air produce a haze, which turns into a fog when water vapour is condensed on the particles, and when sufficient moisture is condensed the fog becomes mist. A mist may be looked on simply as a wet fog. The water-drops in a fog gradually settle on exposed surfaces, but in order to ascertain the extent 1 to- which moisture is present, it does not suffice- to take account of the drops falling on an exposed- surface, as these are often dry, though moisture' may be abundant, as the drops which do fall are very small, and evaporate very rapMly from the surfaces heated by radiation. The instrument as used for numbering the drops by Mr Aitken consists of a glass micrometer divided into squares of known size, a spot mirror for lluminating, and a strong lens or microscope

for observing the drops on the stage. In one fog in which objects beyond 100 yds were quite invisible and the surfaces of exposed objects were quite dry, the number of drops' falling per minute varied greatly, sometimes numbering as many as 3000 per square centimetre; sometimes as few as 300; while on another occasion, with similar conditions of fog, 1300 were noted. Another form of the apparatus permits the counting of the drops which fall from a column of air of known height. It ig well known that many substances have the property of phosphorescence after exposure to sunlight, and M. Becquerel, the great French soientist, who lately died, made a study of this interesting subjeot, and gave a list of substances which showed this remarkable property. But as early as the seventeenth century Robert Boyle called attention to the fact that a diamond, will phosphoresce Biraplj by the heat of the hand, and that it will emit light on being rubbed. Some recent experiments made by Mr Kune, a well-known expert in diamonds in New York, show that all diamonds will emit light when rubbed in the dark on cloth or metal ; and it is believed that the property may prove of great value in distinguishing between the tiue diamond and other stones which imitate it. It is pointed out that the phenomenon is evidently not of an electrical nature, or it would not show itself when the stone is rubbed on metal. — Another new preparation which may prove to be of use in medicine is " microci- | dine," described by Dr Berlioz, of Grenoble. It is a white powder, obtained by adding to refused beta-naphthol half its weight of caustic soda, and allowing the mixture to cool. It is soluble in three parts of water, and while its antiseptic powers are inferior to those of corrosive sublimate or naphthol, they are 10 times superior to those of carbolic acid, and 20 times superior to those of boracic acid. —A new method of purifying impure waters has been brought out by means of that form of sulphate of iron known as ferric sulphate. Ferrous sulphate is now well known as a disinfectant, but does not lend itself as well to the actual removal of foreign matter from water as the ferric sulphate does. Hitherto the objectiqn to ferric sulphate has been its cost, but a process has just been devised whereby it can be manufactured directly from roasted pyrites, which is a mere waste product at so many mines. The ferric sulphate is more effective and cheaper than milk of lime, which is the substance in most general use for throwing down impurities from water. — Lamp chimneys and other glass articles liable to frequent, excessive, and sudden variations in temperature are found to be very durable if subjected to the toughening process invented by La Baßtie. This consists in heating the glass nearly to malleability, but not hot enough to lose its shape — say 1400deg. This glass will withstand sudden changes of temperature without damage, even to the extent of the pouring of molten lead into a tumbler. The strength of the glass is said to be increased many times.