SCIENTIFIC.

Otago Witness, Issue 1906, 21 August 1890, Page 41

SCIENTIFIC.

—Most persons would say that the outside light is two or three times as strong as that within our houses. But the ratio of difference is vastly greater. Carefully prepared tables, according to Health, show that for a view at the seashore, comprising sea and sky mainly (with a lens and plate of a certain speed), an exposure of one- tenth of a second is sufficient. An open landscape away from the sea would, with the same lens, the ssme aperture, and the same plate, require one-third of a second. A fairly lighted interior would- require two minutes and a-half, while a badly lighted interior, such as , rooms which most, ladies prefer to occupy, would require: talf an hour to obtain an equally good picture. In other woids, patients strolling on the seashore in ' sunny weather are in a light not two or three times' but 18,000 timesstronger than that in the ordinary shaded and curtained rooms of & town House ; and! the same patients walking along the sunny side of a street are receiving more than 5000 times as muoh of the health-giving influence of light as they would receive indoors in the usually heavily curtained rooms. — An important find has been made in Egypt by Mr Petrie of the remains of two small towns, one of the date 3000 8.0., and the other of date 1000 8.C., which ought, when properly explored, to throw a deal of light on certain points in the history of our civilisation. For example, it is shown for the first time how the ancient Egyptians obtained fire, and their method was practically identical with that practised by certain of the Australian aboriginals who used a wooden drill which, on being caused to pierce rapidly a piece of inflammable wood, produced flame. A couple of wills have been found, one of which indicates the satisfactory social condition of women in these old times, for in it a husband bequeaths the life interest in his property to his wife, and empowers her to divide the property as she pleases among their children. It appears that 3000 years ago the modern shoe was beginning to be evolved out of the sandal, but the boy's pegtop and tipcat were as far advauced as to-day, and the girl's doll enjoyed even then the luxury of jointed limbs. These matters are mentioned merely to illustrate the detail with which ancient , life in Egypt is going to be opened up again. — An interesting . study lias been lately made by Herr Tarchenoff of electric currents in the skin from mental excitation. Unpolarisable clay electrodes, connected with a delicate galvanometer, were applied io various parts— hands, fingers, feet, toes, nose, car, and back, and after compensation of any currents which occurred during rest, the effects of mental stimulation were noted. Light tickling with a brush caotes, after a ■ few seconds' period of latency, a gradually increasing strong deflection. Hot water has a like effect ; cold, or the pain from a needleprick, a less. Sound, light, taste, and smell stimuli act similarly. If the eyes have been rclosed some time, mere opening of them causes a considerable • deflection from the skin of the hand. It is remarkable that •these ekin currents also arise when the sensations are merely imagined: Mental effort produces currents .varying with its amount;. If a person is in tense "expectation, the galvanometer mirror makes irregular oscillations. In all; the experiments it appeared that, wit^i equal nerve excitation, .the strength o£ theskin-enrrents depended on the '. 'degree to which the part of the akin, bearing 'the • electrodes was furnished with sweatglands.—^Electrician. : — Have we ! really entered: np6n the age of aluminium ? It is the most abundant of all the metals on the earth's crust, and ever ■ since its discovery every leading metallurgist and chemist has been working to find a cheap process for reducing it. In a large measure they have succeeded. Only a few years ago this metal cost more than gold. To-day, thanks to the enterprise of Americans, it has been reduced to the price, block for block, of nickel. At 2dol per pound aluminium is a cheaper metal to use than, nickel. It is nearly four times lighter than . nickel, and will ;go, therefoie, nearly four times as far. Aluminium . has only been on the market in a commercial way for about ' a year. In that time the applications to which this metal can be economically put have been found to be numerous. Its intro- . duction will mark a great step in the advance of human progress. Aluminium at a shilling a pound, and it will surely reach that price, will take the place of iron and steel in many important lines of manufacture. Its adaptability to ship-building becomes at once apparent. The use of aluminium for this purpose would change the mighty black racers of the Atlantis into bright silver vessels whioh would inspire the marine poets to flights of hitherto unheard-of fancy in describing how " lightly the silver ships rode the blue billows." Seriously, there is a possibility that ocean racers in the course of time will be constructed of aluminium. — The niture of bacteria was for a long time doubtful, but it has recently been determined that they are vegetable rather than animal, occurring in four forms — spheroidal, ovidal, , rod-shaped, and spiral. So minute are they that 1500 of them placed end to end would only cover a space equivalent to one-quarter of the head of a pin. They are composed of a granular watery mass, surrounded b- thickened walls. A drop of water is the ocean in which they live. Among their functions is included a marvellous power of reproduction ; in 24 hours one bacterium will produce over over 16 millions. —Lord Rayleigh, in a recent lecture at the Royal Institution, took for his text the word "Foam," and he proved by many interest ing experiments that foaming or frothing is not possible with a liquid of pure constitution. Thus, pure water and pure alcohol will neither of them foam. Water impregnated with camphor, or with a small quantity of any colloid substance, will froth freely; and we all know that a little soap added to water will cause the same effect. Alluding to sea foam, the lecturer said that this was not due to the salt contained in the water, but rather to the seawe' ds which suffer destruction in stormy weather. He also alluded to the effect of oil upon troubled waters, and pointed out that although in the first instance only the smaller ripples were affected by the oily ooating, the larger waves were

afterwards brought under control, for it seemed as if the power of the wind to create those large waves was due in great measure to the small ripples which formed at their back, and gave the wind a hold on the water which it would not otherwise have. It was in reality the curling topß of the waves and the broken water which was mischievous, and this was quieted by the action of the oil.