Scientific and Useful

New Zealand Graphic, Volume XL, Issue 4, 25 January 1908, Page 38

Scientific and Useful

POSTCARDS AS BAROMETERS. A formula was recently published for naking postcards which would by a certain change of colour forecast the weather of the immediate future. In fine weather they appear of a slight blue tint, in changeable weather lilac, and in rainy weather pink. An ordinary developed card should be hardened by immersion for ten minutes in a 5 per cent, formalin solution, washed and dried. Thirty grains of ordinary cooking gelatine should be soaked in water for half an hour, then melted by the aid of heat, and 10 grains of cobalt chloride and 100 drops of glycerine added. The card is flowed or painted over with this solution while warm, excess is drained of!, and the card dried. 4 4 4STREE'J PHOTOGRAPHY AT NIOHT. If one can but withstand the chaff of passers-by and the embarrassment of a gaping circle of onlookers, photographing in city streets at night is a wonderfully fascinating pursuit. It should be remembered that people walking about in front of the lens will not show in the picture as long as they keep moving. Should one of these pedestrians come to a halt in a well-lighted portion of the< view it is well to hold the slide or drop the focussing doth over the lens until he passes on. A street ear or carriage carrying lights should be given the same treatment until it passes out of view, or each light will form a dark streak on the negative and a corresponding light streak on the print. This is all the more ..noticeable if isocromatie plates arc being psed. WOMAN’S WORK IN GERMANY. By a recent census it appeared that of some twenty-six.million women in Germany , tewnty-five per cent, were wageearners, as against seventeen and fivetenths per cent in the United States. One-third- of the entire number of German working women were . engaged in agricultural pursuits. Recently it was true that there. were only nine women physicians in Germany, as compared with seven hundred in Russia, and five thousand in the United States. The admission of women to the German universities will effect a great change in the ratio of the number of women engaged in professional pursuits to that of the women engaged in agriculture. ♦ ♦ ♦ FLOATING DOCKS. Considerable development has occurred in recent years in the provision of floating docks. Docks of this character are actually in existence, or are.under construction, which are. adapted for dealing with the largest ships of war and the most capacious liners. Our own navy has a floating dock at Bermuda capable of lifting warships up to 10,500 tons dead weight, anjl the navy of the United States possesses docks of even greater lifting power. On the commercial side a floating dock is being constructed capable of lifting ships up to 30,000 tons dead weight, thereby possessing sufficient power and dimensions to deal with vessels of aboijt the size of the new Cunarders. It is claimed for floating docks, and, of course, rightly so, that they are distinctly eheiyier than graving docks, and can be built much more rapidly. It has also been stated by Mr. Lionel Clark, who has done so.mueli for this system of construction. that there are docks of this character at present in existence- which have been working for over forty years. Those which are self-docking, or can be docked, arid which have been carefully looked after, are, he says, still in good condition. Others, which have never

been docked, but allowed to slowly deteriorate, are now practically worn out. To compare such docks with graving docks the conditions of the site and the nature of the accommodation to be provided will, on careful investigation, generally indicate in which direction the balance of advantage lies. The two types are not rivals, and there is no question of one supplanting the other; they are both efficient, each possessing its own special features, and it is for the engineer to examine carefully these points as circumstances arise, and to decide which of the two is the more suitable for his purpose. —“ Engineering.” 4-4-4 INFECTIOUS MEDICINE BOTTLES. There is good reason to believe that infection is sometimes spread by medicine bottles, which, after having served their purpose in the room of a person suffering from a contagious disease, are put to other uses. A short time ago the National Glass Bottle Workers Trade Union sent a deputation to the President of the Ixieal Government Board to draw his attention to this danger to the public health. Mr Burns promised to consider the suggestion of some restriction on the sale of secondhand bottles collected from rubbish heaps and elsewhere, with a view to enforcing perfect sterilisation. The German Pharmaceutical Association, at its recent annual meetin, discussed this question of secondhand bottles, and it was resolved to petition the Government to prohibit the return to chemists’ shops of bottles previously supplied to customers suffering from contagious diseases. The resolution was the outcome of two cases in which employees of chemists had contracted diseases as a result of washing. infected bottles. In Austria, physicijliis already insist on the use of new bottles for their prescriptions, and in America 1 ’ a chemist’s assistant recently claimed damages in respect of an attack” of scarlet fever, said to have resulted' from handling medicine bottles returned from scarlet-fever patients. 4 4 4 THE SMALLEST SCREWS. The smallest screws in the world are those made in watch factories. They are cut from steel wire by a machine, but as the chips fall from the knife it looks as if the operator was simply cutting up wire for his own diversion. One thing is certain: no screws can be seen, and yet a screw is made by every third operation. The fourth jewel wheel screw is next to invisible, to the naked eye resembling a speck of dust. With a glass, however, it can be made out quite distinctly. It has two hundred and sixty threads to an inch. These little screws are four one-thousandths of an inch in diameter, and the..heads are double in size. It has been estimated that an ordinary thimbje would hold one hundred thousand of them. About one million of them are manufactUred in the course of a month; but no attempt is ever made to count them. In determining the number, one hundred of them are placed on a very delicate balance, and the number of the whole quantity calculated from the weight of these. All the small parts of the watch arc counted in this way,, probably fifty out of the hundred and twenty. When they have been cut. the screws are hardened and put into frames, about one hundred to the frame, heads up. This is done very rapidly, but entirely by the sense of touch instead of by sight, so that a blind man with a little experience could perform the task. I he next step in the process is to polish the heads th an automatic machine, ten thousand at a -time. The plate on which this is done is covered with oil and a grinding coinpound, rind on this the machine moves them very rapidly, by a reversing motion, until tlicy are in perfect condition.