SCIENCE NOTES.

Otago Witness, Issue 2373, 24 August 1899, Page 54

SCIENCE NOTES.

— Probably very few of those whose know- , .ledge is derived from such studies as they Jiave made at school or college could accurately express the commonly-accepted theory as to the cause of the regular tides. That fche moon drags the ocean away from the ; earth on one side, and the earth away from the ocean on the other, is, says the Morning Post, the general impression likely to be left I on our minds by the perusal of the usual chap- ] ten, on the subject in our text books. Yet this idea, which has much to s-upport it in the writii>g-> of home very leaj-ncd authorities is, iv the opinion of Mr J. JV. Moi-loy, who

has just issued an' interesting book «ntitl«d "The Tides Simply Explained," "too absurd to deserve any answer." He believes that the true explanation of the tides, in accordance with the laws of Nature, has never yet been understood, and he is borne out by the statement appended to the Admiralty Tide Tables, that " there are few physical subjects which are still at the present time on the whole more unsatisfactory." Mr Moxleys object is, to prove that the tide is caused by pressure. "In my view," he writes, " the tidal force of the luminaries cannot draw the water horizontally, and still less can it lift it vertically, or cause it to lose contact with the earth. . . . What field of action is open, to them in this matter? I reply, that of increasing gravity over one region of the' earth, and of counteracting — that is, in effect, lessening — gravity over other regions." Mr Moxley supports his argument by a mass of facts and figures, which possess a, great deal of interest for any reader who is .genuinely attracted by scientific discussions. — One lesson which the Spanish-American war has thoroughly taught is the vital importance to a nation which would have an efficient navy of the fostering of the mechanical instinct. Americans may be proud of bein* a nation of mechanics, and I attribute the overwhelming victories over the Spaniards largely to this fact, and the absolute lack of any mechanical aptitude on the part of the opponents. The utter failure of Cervera'sfast armoured cruisers, which had trial speeds of 20 knots, to escape from the United States vessels at Santiago, none of which were making 17, shows the disastrous results of discouragement of the mechanic. As we know, the condition of the two fastest ships at Santiago — the New York and Brooklyn — was such that only half power could bo used immediately, and it seems almost certain that, had Cervera's ships been able to make their maximum speeds, they would have escaped. — Engineer-in-Chief G. W. Melville, U.S.N., in the Engineering Magazine for March. — Everybody dreams more or less, but have you ever reflected upon the fact that people who are born blind have only " hearing " dreams? In other words, their mental eye sees nothing; they only hear sounds. This interesting point came up before a scientific society the other Jay, and it was found that of 200 blind persons who had been questioned on the subject, those who had been born without sight, and those who had become blind before their fifth year, never saw things or faces in their dreams. On the other hand of those whose sight was 'osfc between the fifth and seventh year, some did and some did not see in their dreams, while all whose eyesight was destroyed after the seventh year had quite as vivid dream visions as seeing people. Blind persons, it may be observed, dream just as frequently as do normal people. —At 60 miles an hour the resistance of a train is four times as great as it is at 30 miles — that is. the fuel must be four times as great in the one case as it is in the other. But ill 60 miles an hour this fuel must be exerted for a cfiven distance in half the time that it is at 30 miles, bo that the amount of

power exerted and steam generated in a given period of time must be eight times ac great at the faster speed. This means that the capability of the boiler, cylinders, and other parts must be greater, with a corresponding addition to the weight of the machine. Obviously, therefore, if the weight per wheel, on account of the limit of weight that the rails will carry, is limited, a point is soon reached where the driving wheels and other parts cannot be further enlarged, and then the maximum of speed is reached. The nice adjustment necessary in the various parts of these immense engines may be indicated by some figures as to the work performed by these parts when the locomotive is worked at high speed. Take a passenger engine on any of the big lines. At 60 miles an hour a driving wheel s£ft in diameter revolves five times every second, so that the reciprocating parts of each cylinder, including one piston, piston rod, crosshead and connecting rod, weighing about 6501b, must move back and forth a distance equal to the stroke (usually 2ft) every time the wheel revolves, or in the fifth of a second. This weight starts from a state of rest at the end of each stroke of the piston, and must acquire a velocity of 32ft per second in one-twentieth of a second, and must be brought to a state of rest in the same period of time. A piston 18in in diameter has an area of 254£ square inches. Steam of 1501b pressure per square inch would therefore exert a force on the piston equal to 38,1751b. This force is applied alternately on each side of the piston 10 times in a second. — A remarkable engineering feat has just been completed at Buda-Pesth, this being the erection of a bridge, with a 900 ft span, entirely by the aid of electrical machinery. The iron girders employed as piles to keep the water back from the excavations for the shore pillars were driven in by an electric ram, this being in effect a gigantic hammer with a velocity of 12ft per second, and a rise and fal) of about 34-ft. The waste removed from the excavations was raised by an electric windlass, and the water by seven centrifugal pumps working without cessation. —In a recent lecture at the Royal Institute, Sir Robert Ball, the eminent astronomer, stated that wo now know the existence of 30,000,000 of stars or suns, many of them much more magnificent than the one 1 whioh gives light to our system. The majority of them are not visible to the eye or even recognisable by the telescope, but sensitised photographic plates have revealed their existence beyond all doubt or question, though most of them are inconceivably distant, thousands or tens of thousands of times as far off as our sun. A telegraphic message, for examnle, whioh would reach the sun in eight minutes, would not reach some of these stars in 1800 years. An average of only 10 planets to each sun indicates the existence within the narrow range to which human observation is still confined of at least 30,000,000 of separate worlds, many of them, doubtless, of gigantic size, and it is nearly inconceivable that those worlds can be wholly devoid of living and sentient beings upon them, probably mortal in our sense, illustrating the insignificance of mankind. — Vegetables and flowers have their noxious tenants. Certain microscopic fungi which .grow on sick plants can produce actinomycose and other ailments in men. Cancer arises sometimes from a vegetable origin. Senor Domingos Friere. of Rio Janeiro, famous for his inoculations against yellow fever, has found that even flowers are infected with dangerous microbes. Flies and wind spread the infection. Tho rose (Rothschild variety) swarms with the leptothriv ochracea; the Rosa Gallica has a microbe like streptococcus pyogones, and another like streptogallus. Other flowers have colonies not well determined. It is considered not unlikely that the colours and perfumes of some flowers are due to microbes, for the light red of the Rothschild rose is the colour of the leptothrix; and the yellow Hibisous has a yellow microbe. The moral is to smell flowers at a safe distance. — Aluminium is generally supposed to be unaffected by acids. Mr A. Witte, in a communication to the Paris Academic dcs Sciences, proves this belief erroneous. The apparent indifference of the metal to such reagents, he "states, is due to the fact that in their presence it clothes itself with an impervious layer of alumina, but if means are provided for its removal or its formation prevented, the aluminium readily dissolve?. For instance, a solution of common salt and ascetic acid acts on tho metal quite rapidly, the solution having the power to dissolve the alumina and expose tho clean metal tc oxidation. — The new Nernst electric light is creating interest in England, on tho Continent, and in America. Professor Nernst has, indeed, achieved a wonderful result by the very simple means of rendering an insulator a conductor by heating it. The knowledge that an insu-' lator could be made to conduct electricity by heating it was known, says the Scientific American, some 23 years ago, but apparently no one thought of the simple expedient of

heating a very good insulator, then applying a current of suitable potential, and biius obtaining a brilliant light. _ The result is clearly of great commercial importance, aside from its being interesting from the purely scientific bide. The Nernst light appears to have very practical advantages. It can be made to run singly on a pressure of from 500 to 1000 volts, and any lamp which can be worked with voltages higher than those possible with the present glow lamp must bring about great economy in the electric supply. It does not require a thin glass bell and a vacuum, and thup wo get rid of a very

serious difficulty, because these bulbs are very fragile and easily destroyed. In the ordinary incandescent lamp many of them are defective, owing, not to a fault in the filament, but to an imperfect vacuum. Of course, a lamp of the Nernst type would not need regulating machinery, and no trimming would be necessary, and on thi6 account it would appear that an ideal form of street lighting has, at last, been found. The possibilities of the carbon filament are about exhausted. There has been very little improvement for a long time, and it is a remarkable thing that just when the carbon filament was failing to meet the requirements, this new invention should be made, which soems to meet the case. It is very like the discovery of gutta percha at the critical period, which brought electrical cable makers out of their difficulties. As yet the Nernst lamp is in an experimental stage, and it is possible that in time some jf the features which militate against its success will be modified. At present the conducting and light-emitting rod when cold is an insulator, and must be heated with a matoh or by some electrical means. While the Nernst lamp is far from being a commercial success as yet, still it is also far from being only the impractical scheme of an inventor. The lamp js based upon sound scientific principles, which appeal at once to practical electricians, who have been extraordinarily quick in this instance to see the wonderful potentialities of the lamp. The operation of Professor Nernst's apparatus is as follows: — The preliminary heating of the magnesia, A, the professor accomplishes by placing it in the focus of a reflector, 0 (see left figure). On the inner side of the reflector is a spiral wire of platinum, D, which when brought to incandescence by a current produces heat sufficient to render the magnesia a conductor; a current is then passed directly through the oxide by the wire B, and that in the spiral is shut off. A complicated form of lamp is seen in right figure. Here the magnesia, A, is placed within a cylinder, O, which also encloses a platinum spiral, D. As soon as the incandescent spiral has heated the magnesia sufficiently, a current is passed through the oxide by the wire B. Within this circuit is a coil, Gr, which, upon becoming magnetic, draws down the iron bar, E ; thus lowering the now incandescent magnesia from within the cylinder. Upon breaking the circuit the coil loses its magnetism, and a spring, F, raises the iron bar and the magnesia to their former position.