SCIENCE NOTES.

Otago Witness, Issue 2252, 29 April 1897, Page 48

SCIENCE NOTES.

•„" Experiments at the imperial navy yards at Wilhelmshafen have shown conclusively that aluminum cannot be used practically in men-of-war construction, while aluminum bronze has turned out satisfactorily in many case?, when the alloy contained 91 96 per cent, of aluminum and 64 per cent, copper. After investigating and testing aluminum in certain parts of vessels, the following conclusions were arrived at: Aluminum bronze is uielesu for bearings, valves, &c, on aocount of the rapid wearing away; it baa been found useful, however, for various parts of machines where friction U not an important factor, and also in cases

where light weight Ib an object, Furniture made of aluminum showed decidedly too little resistance, and required frequent repainting ; aluminum shows, furthermore, but little resistance to sea water, thus making it useless for the walls of vessels. A 10 per cent, aluminum bronze, however, stands a fair chance of being freely used as soon aa the price of aluminum can be sufficiently reduced to approach the value of cast steel.

• . • In the mining and foundry district of Bochum, Prussia, Dr Nieden reports having treated, daring the years ISBS 94, 5443 patients engaged in each occupations, of whom more than 68' per cent, were cases of iDjnry to the eye in their calling— iron and

foundry workers showing a large predominance in this respect over miners. Of 3723 iron and foundry workers treated for eye irjaries, 2805 were for the left dye and only 1639 for tha right, or a relative proportion of 56 Co 44 ; and as a similar proportion held good in each separate year, the conclusion arrived at is that in such work the danger to the left Bye is really greater than that to the right. Even more marked, in fact, was the proportion in respect to the severe cases, the left eye being quite lost in 17 cases, the right eye in seven. It is urged, therefore, that in iron workers the loss 9t the right eye should be calculated as the more serious, inasmuch as the individual then runs a greater risk of injuring the remaining eye than when he has lost the left. • . • " The small size of the screw," says a noted shipbuilder, " is not due, as you might think, to the 'perception of any inventor of its great effect as compared with a larger one. When I first engaged in the machinery business screws for steamers were made as large as possible, it being the theory that the greater the diameter, the higher the speed. A vessel was sent to sea with a screw so large that it was deemed best to cast each blade in two parts and then weld them together^ Duiing a storm all three blades of the propeller broke at the welding, reducing the diameter by more than twothirds. To the surprise of -the captain, the vessel shot forward at a speed such as had never been attained before. Engineers then experimented with small propellers, and at once discovered that they were much more effective than large ones." • . • Professor Roberts- Austen's discoveries on the interdiffusibility of metals have been taken up by the Royal Society of EDgland. The facts have been to some extent known to savants before, but now the results are made more clear. It is shown that solid metals may be made to mix themselves as if the atoms were living creatures. Professor Boberts-Austen has, in fact, discovered pieces of metal engaged in the very act of mixing themselves up with each other. Of course, the interest of this is that the interdiffusion had been found to take place when the metals were cold, and though this property in metals, to ba capable of attaching themselves one to the other when cold, has been talked about before, nothing so clearly proved has* hitherto been at the service of metallurgists and chemists as the facts adduced by Professor Roberts-Austen. He shows that when clean surfaces of lead and gold are held togstber in the absence of air, at a temperature of 40deg for four days, they unite firmly, and can only be separated by a force equal to one-third of the breaking strain of the lead. The professor has also proved that if a plate of gold be laid under one of lead about three-tenths of an inch thick, in three days gold will have risen and diffused itself to the top of the other metal in very appreciable quantity. • . • A most novel and ingenious method of adding the representation of a rainbow to stage realism has recently been discovered, the effect which is produced being as beautiful as the means employed are simple. The apparatus consists of an ordinary box, having a semicircular opening in front to give the shape of the rainbow, within which are two candelabra prisms, mounted on supports, so that they can be revolved by means of handles fixed outside. To work the apparatus a strong light is projected through the prisms and through the opening, across which strips of wire are fixed in order to break up the rays, and thence on to a backdrop scene. When the prisms are turned in opposite directions it is asserted that the most beautiful and vivid colour-effects are produced. • . • Dr Ranke, of the Garman Anthropological Sooiety, recently undertook to describe the physical characteristics of the earliest men, as ascertained from the examination of pre-historic graves. They were of a yellowish colour, he said, and had coarse hair. Their

beads were peculiarly shaped, the part of the sknll which contains the brain being large while the face was small. They had other peculiarities, among which was the mdi I mentary or undeveloped condition of the third molar, or back grinder tooth. The dootor believes that the first men originated in Asia. • . • How suggestive the vegetable kingdom is of engineering problems was pointed out in a very interesting manner some time ago by Sir Benjamin Baker in a presidential address to the British Institution of Civil Engineers. " Every .tree," he remarked, "is a vegetable pumping engine, but hydraulic engineers would be sorely puzzled to explain how the large quantity of water required to supply the evaporation from the extended leaf service is raised heights up to 400 ft and above. We know that the source of energy must be the sun's rays, and we know further that in the production of starch the leaf stores up less than 1 por cent, of the available energy, so that plenty remains for raising water. Experiments have shown that transpiration ac the leaf establishes a draught upon the sap, and there is reason to believe that this pull if? transmitted to the root by tensile stress. The idea of a rope of water sustaining a pull of perhaps 1501b per square inch may be repugnant to many engineers, but the tensile strength and extensibility of water and other fluids have, been proved experimentally by Professor Osborne Reynold?, and by Professor Worthirigton and others. A liquid, deprived of air, entirely filling a glass vessel, when cooled pulls on the vessel, and at last lets go with a ! violent click. Water has baen so stretched nearly 1 per cent, of its bulk, and the adhesion of the-jwater to the sides oE the vessel and the amount of the tensile strength were found to be quite equal to that of good mortar. With ethyl alcohol the modulus of elasticity, both in tension and compression, vras constant up ro the ultimate tensile resistance realised of 2551b per square icch. Many hydraulic engineers have, no doubt, lived and died without encountering anything in their experience suggesting that water and other fluids 'were capable of reBisting a tensile stress of no insignificant amount; and yet aa long ago as 16G3 the fact whb known, for the secretary of the Royal Society then wrote to tha Governor of Connecticut that • what puzzleth and perplexith us is that water defecated from the air remains suspended and doth not at all subside after the receiver hath been exhausted of air'; and in the Fame year the president was 'asked *to entertain his Majesty' Charles II with the sight of quick- j silver sustaining itself by tension at a height of 50in when the barometer was at 29in, • something eke but equipondency of air being,' it was truly said, ' necessary to ex- ; plain this odd phenomenon.' " i