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Otago Witness, Issue 2416, 28 June 1900, Page 62

SCIENCE NOTES.

•* — All artificial lights, even the best, are extravagantly wasteful of energy, in that they , iavi&h it in the infra-red, and not in the vibi- ' ■bit* ' spectrum. Mr C. G. Abbot, who has charge of the Astrophyaical Observatory of; tho Smithsonian Institution, lias examiued I the light emitted by the Welsbach mantle (which" consists of impure thorium oxide) and other in-:.indesceit mantles, by means of the bolometer, with a view to coir.pr.ring their tsfxicipneiss. Though il«e illuroinaxicg powers differ oonsideiably, the distribution oi enevgy is much, lew divers fied tlion would be t>upposed, and shows clearly the wosteioluesri even , of the Welebach light as a source of illumination. The'infra-'red in each case includes

by far the greater portion of the energy, and not the visible spectrum, as ,is the case with the sun, and still more with phosphorescent substances. Excluding the infra-red radiation, the Welsbach. mantle was found to be superior in light to the others experimented with, especially in the red, orange, and yellow parts of the visible spectium.

— Engineering discuses the problems of submarine boats, and points out that they have no buoyancy, and their low longitudinal stability or tendency to pitching i& a matter of serious moment. A man need only "step forward to send the nose of the boat down. For this reason the Plongeur of Bourgeois failed, and thfe length of boats has been reduced again. Goubet has gone fwihc&fc in this direction, and his two men always sit in the middle of the boat. Bauer tried to apply counterpoises and Holland automatic puvnps, to restore longitudinal equilibrium. Nordenfeldt did not deprive his boat of all buoyancy, and counteracted its effect by a submerging propeller. The flooded boats are better off in this respect. But even in their case v/e notice a reduction in length ; the Zede had a length of 45 metres, the Morse of 35 metres, the Narval cf 34- metres. It lias, o:\ the other hand, been pointed out that they are not good sea-going boats, hardly fit for rough weather ; and thfcir own designers have proposed to give them a little freeboard. If we do that, we lose the chief advantage cc the submarine boat, the immunity against projectiles ; and we may argue whether we had not better return to ordinary boats, in -which we are not tied down to small space and unal! fcpeed, and all Eoris of undesirable -conditions. Submarine boats remain dangerous to manage. On the average, perhaps, we construct them strong enough to descend to a depth of 100 ft. Supposing a boat, moving at the usual speed under water, eight kuois, is to discharge a torpedo. Two men are sent forward ; tho boat ;>t once inclines 15deg, and within Lolf a minute it -will have arrived in its critical depth. If there is any delay or any fault in the steering gear or in the application of safeiy weight? 1 , etc., every Eecond will seriously increyte tho pleasure of the water outside. T/iate made with the Gymnote, moreover, indicate that wkvarine boats

do not obey their horizontal helms with sufficient rapidity. The Gymnote alwa^-s overshot her mark, and would not keep on a etraight course, but described a succession of curves. Professor Busley, a German expert, iried to pull a submarine boat under water ; it could not be done when the spsed exceeded four knots. That all operations near the coast or in shallow water are exceedingly dangerous need not be emphasised. Campbell's boat managed to wriggle herself out of the Thames; mud again h\ 1886; the accidenttestified to the nerve and_ skill of Lord Charles Beresford. but also to his good luck. These dangers are increased by the exceedingly limited range of eight under water. On a clear day, a diver, 20ft below the surface, is hardly able to &cc further than ?,sft. The low speed and the short period during vthich such a boat can be kept in motion without replenishing its charge limit the range of action or the submarine boats badly. The Narval is stated to have cost about £30, C00. "For little more, Engineering adds, we could construct a torpedo-boat destroyer of four-fold epeed and ihieelold displacement which would achieve something.

—At a recent meeting of the "Royal Society in London a paper was lead which dealt with a remarkable investigation undertaken by Professor Dewar, Sir James CrichtonBrown, and Professor Macfadyen. The in quiry wa« held for the purpose of ascertaining the effect upon disease-causing microbes of immersion in liquid air. Liquid air, we may remind our readers, lias a temperature which M'oulcl be represented on Fahrenheit's thermometer by no less than 34-4deg of frcst ; and it might reasonably be supposed that no bind of life, animal or vegetable, could long cxi&L in its near neighbourhood. It was found, hovever, that the hardy microbe v/a" none the vrorfce after 20 hours' immersion in the liquid. Certain photogenic or light -giving bacteria qu.-2nch.ed their luminosity when placed in the liquid air, but resumed their customary latSi'inee upon being removed and warmed to the normal temperature. _ Similar experiments are about to be carried out with liquid hydrogen, the temperature of which is considerably lower. — A most interesting series of elaborately illustrated articles has recently appeared in the Scientific American (Supplement), entitled "The Home-made 'Windmills of Nebraska," by E. H. Barbour. It would seem that the farmers of Nebraska, led by some ingenious fellow, have made rough but efficient windmills, chiefly for pumping water, and that thetsc arc common all over the district,. They are matte of wood, mostly of any waste lumber that happens to be at hand ; and come of them have cost less than 10s, and yet are doing valuable service in irrigation. These milk \ery from one-man to eight or ten hor?e power, the larger ones being employed for all purpose-. Although ibey do dot seem to have been used for the production of electricity, it is clear that in connection with a dynamo and nccmmulator, which le.tter could be, charged in the daylight hour?, these mills would do good service. The system is worthy the attention of all who live in country -districts, despite the obvious disadvantage of wind-power — its inconstancy.

— An interesting article in the April number of Pearson's Magazine describes the wonders of tele-photography, a tele-photograph being a view taken at a great distance, pe*'hans miles from the object, and yet showing as many details as though the lens had been exposed at close quarters in the ordinary way. '"The tele-photo lens," the writer remarks, "has been playing an important pare in the Transvaal war. Soon after the war broke out it was announced that tele-photography had been officially recognised by the War Office, and thai it was to pi ay a part for the first time in a British campaign. Second Corporal Ford, of the Royal 3£r.girsers, Chatham, was appointed tele-pnotosrapher to the Army in youth Africa, and sailed from Southampton in November last with "his apparatus and the now indispensable Hcycle. The apparatus can be fixed on to the bicycle in very small compa^, and as both bicycle and apparatus are painted khaki colour, they do not present a very prominent mark to the enemy. The tele-photcgraphic camera, under Corporal Ford's direction, proved valuable in scouting work that the War Office determined to make greater use of its services. and with that end in. view a more perfectly equipped party of tele-photographers— seven men in all from the Eoyal Engineers— was despatched to South Africa. Their outfit consisted of a large fle-photographic camera, capable of taking a clear picture of anything ■within range of three lrile 5 :, ana a number of smaller cameras for othei work, together with a printing waggon Sited wi'h a dark room and all the ch&rcicsl solutions required in developing, toning, and printing. _ Telephotography has many xibos in war. in the first, piece, it is an immense advantage to thp photographer who is taking a view of actual fighting to be able to iokce himself at a safe di&lanca away from the fire oi the enemy. Wai correspondents hove been killed in action before now and the bnHct is no respecter of pcr&ors on the field of battle. Secondly tele-photography is useful to the general in command." for he thu^ hps the means of quietly studying the eaemv's movements, their camps, fortifications. emrnich;nents, arid Vihai not, from nhoto graphs, taken at a distance of several mile*. Tele-photography from a balloon has been often attempted wuh very successful results, especially in tha Italian army. Thus, by its use. officers of ilie TtaHan Engineers have been able to discover in the Alps French battfi'ies which had bolox'o been unknown to th<!m, and to observe clcorly the details of their construction. Tue tolo-pLoro lens was used by the Ja«£>neP3 Government in their war with China -.nth marvellous ros,ulc=\ One of the mo&t ctrikmg was obtained by on official photooranhor of the Jnpane?s War department, at a distance of upwaivl-j n-i two miles, pncl rho*F. the Tel-Yen, one of the two largest ve^oL in the Chinese navy, with a displacement, of 7300 lon*, mid with steel plates 14in_ thick, aftci she had bevn halfsunk by a .'apanesc torpedo beat. The vessel lay' far beyond the reach of any ordinary lens, and yet the tele-photo showed net only the ship, but s\ho, quite plainly, the effects of the torpedoes and cannon phots against her sides."

— Amoug the new instruiiionls brou<;hL out by Mcew Iscntfial, Poisder, and Co., for use in connection with radiography and wirelco telegraphy, its a mercury \el interrupter, which* is said to be one ol the ment perfect forms cf break yet do.ugned, and more serviceable than Wehneib'& interrupter. It consists es&enUally or a fine jet oi "mercury forming one control niece, and a bevies of teeth cut in a cylindrical surfaceforming the other contact piece. The cylindrical surface surrounds the jot. Its axis is vertical, and "the teeth taper downwards. Hence, when the cylinder is made to revolve by means of a small motor to which it is connected, jonlact is made when the jet impinges upon a tooth, and broken when it comes upon an interspace. By raising or lowering the jet Ax& ratio of contact to in-isi-ruption may be varied from zero to infinity, pad thus the mean, em-rout strength

may bs adjiisted to any required value without interposing resistances. The number r.f interruptions may be varied through a wide range, and within 24 hours contacts and the motor geared up to 3000 revolutions, it reaches 72.000 per eecond, which suffices fo/ practically every purpose. — Nature.