SCIENCE NOTES.

Otago Witness, Issue 2923, 23 March 1910, Page 76

SCIENCE NOTES.

—Ever-growing Teeth.— Certain animals, it has been found, have teeth which grow all their lives. The rat and the squirrel are examples of this. Humar teeth are developed from pulps, which are absorbed and disappear after the teeth are grown ; but in the case of a rat the tooth pulp is perpetual, and is continually secreting material by which it gains length. Therefore, the animal is obliged to gnaw all the time to keep the tooth down to its proper length. It is commonly believed that rats keep gnawing out of pure.mischief, but such is not the case.—Popular Science Sittings. —Hygiene in the Kitchen.— An eminent physician ones said:_ "If I am called in to a case of diphtheria, the first thing I look at is the kitchen sink." The dangers arising from a badly-kept sink cannot be exaggerated, nor can any degree of care in avoiding them be considered extreme. The waste pips from a kitchen sink should have boiling water and ammonia or washing soda poured down it each day. At ieast once a week it should be treated to a dose of some good disinfectant, such as chloride of lime. This old stand-by is very inexpensive, and quite as good as many of the modern high-priced articles. Put a large teacupful cf chloride of lime into two quarts of water, and use as'required for cleansing the sink. —Progress of Languages.— The progress of languages spoken by different nations has just been analysed as follows:—English, which at the commencement of last century, was spoken by only 20,000,000 of people, is now spoken by 100,000,000. Russian is now spoken by 63,000,000, against 30,000,000 at the same period. ' In 1801 German was spoken by only 35,000,00 people; to-day oyer 70,000.000 talk in the same language that William the Emperor does. Spanish is now used by 44,000,000 of people, against 30,000.000 in 1800; Italian by 32,000,000, instead of 18,000,000 ; Portuguese ' by : 13,000,000, .instead of 8,000.000. In the case of French, the. increase has been from 34,000,000 to 16,000,000. or 36 per cent. . —The World's Supply of Iron.— Less than two million tons of ore was mined in 1800, less than 11 millior tons in 1850, and nearly 85 million tons in 1901. Some day the world's supply of iron will be exhausted, and the question, when this day will come, has already been discussed. According to Professor Binz, the total quantity of iron ore contained in knowr and workable deposits amounts to about -8000 million tons, distributed as follows :—Germany, 2200; Russia, 1500; France, 1500; United States, 1100; Sweden, 1000; Spain, 500; England, 250 million tons. As an annual production of 50 million tons of iron means an annual consumption of from 100 to 150 million tons of ore, the entire available supply cf iron ore, as estimated above, will be- exhausted before the close of the twentieth century. Apart from the fact that vast regions of the earth iiavo not yet been explored in' search of the. mineral deposits, this conclusion appears far too pessimistic, for the reason that ores, very poor in iron, which are not now worked, but could be worked in case. of necessity, exist in (great abundance. Hence an exact answer to the question appears to be neither necessary 'nor possible at present. —The Mariner's Compass.— There can be no doubt that the_ Chinese •were acquainted with the directive "property of the loadstone at a very early period. The art of communicating the magnetic virtue to steel and suspending the needk on a pivot is undoubtedly a European discovery. By some writers this is ascribed to Flavio Gioja, an Italian mathematician, who, it is said, improved the compass in the year 1302. The deviation of the magnetic needle from the true north is measured by an instrument called the declinometer. It has been found, however, that this instrument only gives results approximately correct, and it has been superseded in observations by an in--strument called the magnetmeter. Magnetic storms, which sometimes last for hours or even day*, cause irregular, jerking movements of the magnetio needle, and it has been found that magnetio perturbations are most energetic when there are most spots on the' sun. Whether the spots cause the magnetic storms of the" magnetic storms cause the spots is not known. Soma scientists -hold that there is a connection between the two phenomena. —The Phenomena of Sound.— In the Arctic regions persons can converse at more than a mile distant when the thermometer is below zero. In air. sound travels from 1130 to 1142 feet per second. In water, sound passes at the rate of 4708 ft per second. Sound travels in air about 900 ft for every pulsation of a healthy person at 75 in a minute. A bell sounded under water may be beard under 'water at 1200 ft distant. Sounds arc distinct afc twice the distance on water that they are on land. In a balloon, the barking of dogs on the ground may bo heard at an elevation of three or four miles. On Tablo Mountain, a mile above Capetown, every noise in it and even words may be heard distinctly. The fire of the English on landing in Egypt was distinctly heard 130 miles orr the sea. Dr Jameson says in calm weather he heard every word of a sermon at the distance cf two miles! Water is a better conductor of sound than air. Wood is also a powerful conductor of sound, and so is flannel cr riband. Sound affects particles cf dust in a sunbeam, cobwebs, and water in musical glasses; it ebakes small pieces of paper off a string in wncoid. Deaf persons may converge through deal- rods held between the teeth, or he'd to the threat or breast. - —Radium and Growth of Plants.— Soon after the discovery that the Rontgen rays are a component of sunbeams. Prores or J. N. C. Aiuller, of the Berlin Botanical Society, raised the question as to whethc-r oi not the rajs thus occurring exerted any influence upon plants. H"> placed specimens of garden cress in a dark chamber protected from sunlight and found that their steins turned towards the rays. By this means, and also by using pho* phorescent substances. Mullet reached the conclusion that the X rays present in gunbeame do act upon plants. The object of another experiment waa to ascertain the effect of the thorium rays from an incandescent gas mantle on the germination and growth of timothy grass eeeds. Unsoaked rfseeds cf timcthv grass were sown* m a >;r

across the sv-fise of the moist soil in a germinator. Lying horizontally over the seeds a* fight angles to the row and about an inch above, the surface of the soil was the gas mantle. The culture was placed in the dark room of a moist chamber. The seeds shot up very rapidly except directly under the mantle, where was only a very slight germination. The thorium rays of the gas mantle, it was found, retarded the growth of tinicthy grass when the mantle was placed over the seeds germinating on the surface of the soil, but germination ano growth did not appear to be effected hi the least by burying the mantie in the soil: —Comets and Comets' Tails.— The new daylight comet which swam so suddenlv into the ken of astronomers in the northern hemisphere is leaving the earth at the amazing speed of 100 miles a second. "No doubt, like most of its kind, this one is formed cf cyanogen, other carbon compounds, and sodium," said Sir Robert Ball when interviewed at Cambridge the other day. "Comets, however, are practioallv impalpable. Lexell's comet, for instance, in 1770 went through Jupiter s satellites, but they did not show the slightest indication' of any effect. On the other hand, the comet was extremely knocked sbout, and was turned into another orbit. I, in common with everyone, spent two hours in a comet's tail in 1861, and no one knew anything about it until afterwards, when the* astronomers told what had happened." Astronomers agree that though the new comet and Bailey's comet are approaching each ether, they will not collide. They are not moving in the same plane. "It is as likely that they will 'bump,'" Sir Robert said, "as that a rifle bullet fired in Dover would hit one fired in London." The most peculiar feature of comets is the tail. Sir W. H. M. Christie, the Astro no mer-Royal, in his charming little "Manual" published by the Christian Knowledge Seatety, has collected some striking facts with regard to these strange appendages. The tail of the comet of 1861 was 40 million miles long; that of 1680 had a tail of 60. million ; that cf 1811, which was visible for seventeen months, over 100 million; while the visitor of 184-3 showed a tail in the evening twilight of or about 200 million miles, in length—which exceeds the diameter of the earth's orbit. We mentioned the other day, says the Daily Telegraph, a theory of Clerk Maxwell's that when particles of roatiei are of microscopic size, say two or three hundred-thousandths of an inch in diameter, "the sun's light would repel such particles more tha=rr the mass of a comet would attract thorn. This theory has been proved 'to be- true by various experiments; and' the Cambridge mathematicians have shown that if comets consist largely of such fine, gauzy matter-of almost "spiritual texture," to use. Herschel's phrase, this repulsive action of light would account for,, the tails of comets, and fox their common sickle-shape outline. • It would help to explain the apparent break up of cometarv masses, of which there seem to bo real evidence. It is not unlikely the comet of 1910 may throw further light on the remarkable light force, the discovery and demonstration of which is one of the most eminent achievements' of recent physics.