SCIENTIFIC AND USEFUL.

New Zealand Graphic, Volume XI, Issue 34, 26 August 1893, Page 128

SCIENTIFIC AND USEFUL.

to photograph on marble. M. Villon publishes the following process : Coat an unpolished pl ate of marble with the following solution : Benzine 501) parts, spirits of turpentine 500 parts, asphaltum 50 parts, pure wax 5 parts. When dry, expose under negative, which will take in sunshine, about 20min. Develop with spirits of turpentine or benzine, and wash in plenty of water. Now cover the plate where it is intended to be left white with an alcoholic solution of shellac, and immerse the same in any dye which is soluble in water. After a while, when enough of the colouring matier has entered the pores of the stone, it is taken out and polished. The effect is said to be very pretty. A ONCE-FLOWERING PLANT. At a meeting of the Royal Botanic Society, one of the branches of the flowering stalk of Fourcroya sclloa was shown from the Society’s conservatory. This is a Mexican plant allied to the aloes, and like them it flowers only once during its life. The plant, which has been in the conservatory for upwards of twenty years, late last autumn threw up a flower spike, which in a short lime grew to a height of thirty feet, and, passing through the glass roof, rose for some feet into the open air. It could not, of course, resist the frosts and fogs of winter. The flower-buds dropped unopened, when immediately from each node a number of young plants appeared. This mode of reproduction is found in only a few vaiieties of plants, and is especially valuable in relation to the cultivation of fourcroyas as a source of commercial vegetable fibre. UMBRELLA FOR ’CYCLISTS. It should be of interest to ’cyclists to learn that a London firm have produced a novel appliance, which, they claim, will keep the rider dry and cool in all weathers and increase his speed of transit. In short, an umbrella is fitted to the frame of the ’cycle. It is light and strong, the stalk and socket being made of steel tube, and can be, it is said, put up or down in a few seconds, and entiiely removed from the machine in less than a minute. The stalk and socket are enamelled ; it rises and falls in telescope fashion to the desired height, and is kept in position by the pinching sciew. It is finished with a ball and socket joint, which permits it to be angled backwards or forwards or to either side as desired. With the aid of the ball and socket jointit can be angled in any direction to catch the breeze, and thus act like a sail. With a favoniable wind, it is said, the ’cyclist’s umbrella adds from two to five miles per hour to the speed of travelling. THE FLIGHT OF GULLS. Those who have spent a few days at sea can scarcely have failed to observe the flight methods of gulls. They will follow a steamer for hours together with very little effort, if only the ship is going head to wind, or nearly so. For long periods individual birds will advance at ten or fifteen miles an hour without flapping a wing. With a little trouble the observer can easily pick out individual birds in a flock, and he will soon see that some of these fly with much less effort than others. In the structure of the birds there is no difference. If be pursue his investigations, he can scarcely fail to arrive at the conclusion that flight of this kind is not at all a question of power, but of individual skill. Strange as the statement may appear (says an English contemporary), we have not the slightest hesitation in saying that in order that a gull may fly with very little effort indeed, it must be exceedingly skilful, and that certain individuals in every flock are masters of the art of flying, while others are very poor performers indeed. SIGNALLING MARS. A correspondent of the Scientific American says In all the projects for signalling Mars proposed by learned Thebans, I have seen no reference to what seems to the unlearned layman the most self-evident difficulty. It is that the bright side of Mars is always towards us. If signals were sent at night from the dark side of our globe by artificial light, the flashes would have to be of such intensity that they could be seen through sunlight ot that planet. To effect this they would have to be intensely bright. If they could be seen, would the observers know from whence the signals came? Unless their powers of vision are different from our own, they could not see our planet in their daylight. Then much less could they see flashes of artificial light sent from it. Sunlight flashes from a combination of mirrors would have to be sent in the wrong direction. Mars is often in our range of vision in the daytime, but is lost in the brighter sunlight. At rare intervals the planet Venus can be seen by day. Flashes from mirrors might at such times be sent to it. Such flashes would fall on its dark side and would be seen, if at all, by its inhabitants in their night time. A NOVEL COAL-DUST ENGINE. • A novel motive power engine has been patented by a German engineer, and, according to report, Herr Krupp is now constructing a number of experimental engines to test the practicability of the scheme. The idea is to turn to useful account the fact that finely-divided carbonaceous matter floating in the air readily explodes, and to adapt this to the generation of motive power the inventor proposes to grind coal to an impalpable powder, and, after introducing the dust floating in the air into the cylinder of an engine, explode it, the idea being to follow very much the same lines which are being so thoroughly developed in the use of gas in engine practice. The first difficulty which suggests itself is how the ash is to be got rid of, but Herr Krupp says that his experience in gun manufacture convinces him that this is not a serious obstacle. The advantages which would grow out of a direct utilisation of mineral fuel as mined are very obvious. While modern practice converts only 10 to 15 per cent, of the heat energy stored in coal into power at the crank shaft of a steam en gine, it is claimed that no less than 75 to 80 per cent, could be made available by the direct combustion of fuel through explosion of coal dust.