SCIENCE SIFTINGS

New Zealand Tablet, 26 February 1920, Page 46

SCIENCE SIFTINGS

(By "Volt.")

Listening Under Water. The art of listening under water.was brought to perfection during the great submarine hunt of the last years of the war, and it is interesting to know from Professor Bragg, recently lecturing at the Royal Institution, that the first experiments in this direction , were begun less than 100 years ago. In 1826 a bell was immersed and rung under water, and was heard across the Lake of Geneva. Electric bell signals can now be detected- seven miles away under water, and down in the hold of a ship men can hear the sound of a shovel dropped inside another passing ship. Finding Entombed Miners. An instrument invented during the war for finding the positions of underground operations by means of sound has now been put to the use of locating entombed miners. It is a small instrument which detects sounds proceeding through the earth, and by using two instruments in different places the direction from which the sounds proceed can also be found. The little instrument is called the geophone, and miners entombed by a collapse of ground, or by an explosion, will be able to tap on the side of their prison, and the rescue party will be able to find out exactly where they are. World's Deepest Well. One of the seven experimental bore-holes being sunk for oil in Derbyshire (England) has now been drilled to a depth of nearly 4000 ft, according to latest reports. There is a well in South Africa that is over 8000 ft deep, and there are at least a score in the United States whose depths vary between 6000 ft and 7000 ft. The world's deepest well, however, is situated in the neighborhood of Gobelins. Boring was started in 1892, and continued intermittently up till the outbreak of war, when the extraordinary depth of 18,000 ft had been reached, at a total cost of nearly £40,000. Time-saving Signatures. An unusual method of signature is adopted to save the time of directors and officials of a certain insurance company in regard to cheques sent out by the firm. In the case of one signature, all the letters except the last two are lithographed and the last two letters are written. In the case of the second signature, all except the first two letters are lithographed and the first two are written. It is not the first time that this method of signature has been used. But it is by no means common. Directors - and officials of companies whose cheques run into hundreds and thousands a day will appreciate the enormous saving •of time and labor that this method effects. Stopping Fires in Mines. Coal-dust floating in the air in clouds is just as likely to cause explosions in coal mines as firedamp, and there are three ways of overcoming the danger. The commonest method is to use water to lay the dust. Then there is the plan of rendering the dust non-inflammable by mixing with it ordinary rock-dust. This is done by applying a coating of the rock-dust to various parts of the mine, and the plan is very effective. Another way is to set up a trough filled with rock-dust in various parts of the mine. When an explosion occurs the dust is automatically thrown from tho troughs to the floor of the mine, and the cloud « of incombustible dust filling the air at this point stops the passage of the burning coal-dust. Picture-House Tricks. All kinds of instruments are used behind the stage in theatres and picture-houses to produce imitations of noises, such as the clattering of horses' hoofs, the entrance of a train into a station, and so on; and quite elaborate machines have been thought out to produce these noises. Flight has made it necessary to invent still another one, and a new instrument has been produced to make a noise like an aeroplane. Two large discs are fitted together with partitions like a water-wheel, and holes about four inches apart are arranged round the circumference. While one man turns, the "wheel" quickly round, another man pours a jet of compressed air against the holes, and the noise is exactly like that of the motor of an aeroplane in flight.