SCIENCE NOTES.

Otago Witness, Issue 2356, 20 April 1899, Page 54

SCIENCE NOTES.

*— A discussion took place recently at the International Mining Congress at Brussels Jis to the limits of safety to which work can be carried on under compressed air. The Austrian doctors declared that men under 20 and over 50 years of age should not be allowed to work where the air pressure was high, and in all cases medical certificates should be forthcoming as to the. soundness of the heart, lungs, and the .vascular system. An ear affection, a cold, tor a gastric attack should be sufficient for prohibition. The limit of pressure should be 751b, which would enable the work to be carried on under water at 170 ft Ifrom. the surface, but in such cases special precautions would be necessary in returning from the high pressure to the normal condition. The minimum would be 100 minutes, but the men may continue to ■work for any period. It is one of the peculiarities of working under high air pressure that healthy men might almost live in the pressure chamber, but the change from high to lower pressure should take one minute for every one and one half pounds of pressure. Men accustomed to the work might take only 10 minutes for a pressure of 221b, 15 minutes for 371b, or 30 minutes for a 751b pressure. It is suggested that the men in passing through the changes of pressure should suck sugar ; not that sugar possesses any particular Virtue, Tmfc it insures the swallowing of the saliva and prevents the tympanum from Heine injured. As -to "the ventilaficD «f the working "'chamber, the air should be renewed at: the. rate of 700 Hibic feet Der head, per tour*

— Ignorance has of late -years credited science with powers which are comparable only with those attributed to the genii of Arabian fairy tales. Whenever war shows its hideous face we are sure to hear of some daring chemist who professes to have invented a compound which will blow an invading host to pieces. Now it is the turn of the electrician, and we are gravely told that M. Tesla. has discovered a means of annihilating an entire fleet. He has merely to switch on certain currents from ■ a point far beyond the range of modern guns, and the' ships and all that they contain will perish. A moment's consideration will show how idle such rumours are. Powerful as are the machines for the production of electricity, there is none known that will exhibit at one discharge a fraction of the energy let loose by a single flash of lightning. But even supposing that M. Tesla has discovered a rival to Jove's thunderbolts, are we tc believe that the artificial is so much more potent in its effects than the natural article that it cannot be controlled by lightning conductors?

— " Secrets of the Earth's Crust "' is the subject of an article by Professor Cole in the February "number of "Knowledge." We are as yet, he says, only feeling our way on the outskirts of the unseen core of our planet — a core in which iron predominates, but in which other native metals may lie abundantly dissolved. He indicates a series of links which make it obvious that materials once supposed to be meteoric may occur in mass in the lower regions of the earth's crust. It is only in the last few years that geologists have been assured of the presence of considerable masses of native iron in the earth's crust. Nickel iron has long been used by the Eskimo for knife blades and hatchets ; and it was suspected that some large meteorite was being worked as a convenient mine. Nordenskiold, in 1870, observed a block of iron in some ballast taken on board near Godhavn, in Disko Island ; and ir time the true source was discovered by him at Ovifak, a spot difficult of access, but now one of the best known mineral localities in the world. Here, on the .shore, some magnificent blocks of nickeliron were lying exposed to the sea waves. Tho largest, which is now in Stockholm, measures 6ft long, and weighs about 19 tons. . . It is no wonder, then, that the Ovifak masses were at first believed to be meteoric. Even when nickel iron was found in the adjacent basalt of the coast, it was thought chat ■•• meteoric shower might have occurred -\v\iJlr the lava was still hot jyid viscid, and 'that the fragments haox)become consequently entombed. But other discoveries follpwed in the same neighbourhood, notably those o f Steenstrap, ia 3875, and it becama admitted

that the iron was a true constituent of the Miocene basaltic lavas.

— A recent number of the Centralblatt fur Bakteriologie contains a paper on the vitality of the typhoid bacillus in milk and butter, by Messrs Bolley and Field, of the Government Experiment Statical-. for North Dakota, U.S.A. The tmtter used in these investigations was derived from an ordinary creamery, and contained loz of salt per pound. Ten days appear to be the longest period of time over which typhoid bacilli introduced direct into butter could be detected. When, however, the cream was infected with typhoid germs before churning, the latter were discovered in butter even after three months. Typhoid bacilli do not apparently make any marked growth in butter if "-buttermilk is thoroughly worked out of it ; if, however, the latter is left in to any extent, the bacilli take advantage of the mixture and multiply. In sterilised milk typhoid bacteria can exist for upwards of four months, and inoculated into ordinary milk freshly drawn they have been demonstrated as long as "three months. No types of bacteria were met with in milk which proved capable of overcoming the typhoid bacillus ; even when inoculated in comparatively small quantities into sour milk, it took well-nigh complete possession of the liquid, becoming almost a pure culture. These experiments furnish another warning to those concerned with the conduct of our dairy supplies of the supreme importance of vigilance in all matters connected with the manufacture and distribution of such easily infected articles of food as milk and butter.

— Many have been the attempts, by means of propellers and other contrivances, to render a" balloon dirigible ; and although on a very calm day the unwieldy thinghas perhaps been coaxed a point or two out of its course, little has been done to conquer its tendency to sail with the wind and in no other direction whatever. In his attempt to reach the North Pole by means of a balloon, Andree had conceived the idea of trailing behind the car a heavy rope, the object of which was to retard progress, and thus have at disposal a surplus amount of wind which could be made to act upon a small sail placed aslant, so as to alter the balloon's course towards the right or left at will. So as to test this theory, Mr P. Spencer, a well-known aeronaut, recently made a balloon journey over the flats of Essex, carrying with him a ropo 500 ft in length, with a weight of 1001b, together with a square sail of light material. It was found that the new equipment did what was expected of it, arid that it was quite possible to avoid obstacles in the way of the trailing rope by manipulating the guy ropes attached to the sail. The trailing rope was also found- to act as a splendid brake when the final descent was made, the car eventually touching the ground without the usual bump. The balloon was that which has been making captive ascents from the Earl's Court Exhibition (London) for some months past.

— • Dr Frederick Strange Kolle has devised a method of copying letters and print by the "X " rays. The process enables a person to obtain copies without revealing the document to a printer or lithographer. The document is written, or printed, with mucilaginous ink, or varnish, wlych is dusted over with opaque metallic dust, such as mercury biniodide or zinc oxide, before it is dryl The excess of powder is blown off. A block of sensitive photographic plates is then taken, and the document to be copied placed over it. The " X "' rays are brought to bear on the print, or writing, and the ink being impervious to them photographs of the writing, or print, are obtained. An exposure of lOsec or 12sec is enough to give 100 photographic copies. One "X " ray tube can serve for 20 blocks, or 50 sheets, and thus give 10Q0 imnressions in lOsec, or 6000 in a minute. The best plates to use are, in Dr Kolle's opinion, gelatino-bro-mide films. White letters on a dark ground are got by using an ink of red lead, gum arabic, glycerine, and water. For print a semi-fluid mixture of red lead, potassium bromide, and glycerine made into a paste is recommended. An "unfatty" ink yielding black letters on a white ground is made of bichromated mucilage not exposed to light before its use. This method of making copies may be suitable in diplomatic and Governmental departments for secret -"documents.