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From the July 18, 1931, issue

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AIR VIBRATIONS IN ORGAN PIPES REVEALED BY PATTERN IN SMOKE

Making smoke rings in organ pipes, to show up the little cyclones that whirl in them when obstacles are placed in the openings, is the curious mode of research adopted by a London physicist, Prof. E.N. da C. Andrade of University College. These little cyclones, or vortices, have important effects on the tones of the pipes. By photographing them in smoke, Prof. Andrade is able to check the accuracy of mathematically calculated theories never before tested.

His smoke method is an improvement on the one previously in use, which was devised by a German scientist named Kundt. The Kundt method employs dust, but since dust particles are much bigger and heavier than smoke particles, the older method is less sensitive.

Prof. Andrade is engaged in an investigation of what happens to the air in such musical tubes as the pipes of an organ when they are producing their tones. He has found that the smoke particles show by their motion the exact motion of the air. The circulation of air in such tubes had been predicted by the late Lord Rayleigh but was never shown before.

The most beautiful photographs are obtained when a small obstacle is placed in the path of the air currents. New vortices are formed in the neighborhood of a cylindrical barrier in a way that is very striking and cannot be easily shown by any other kind of experiment.

TIDES YIELD CONTINUOUS POWER IN ENGLAND EXPERIMENTAL

PLANT

An experimental power plant that generates electricity continuously from the ebb and flow of the tides has been constructed and successfully operated at the Avonmouth Docks in the Bristol Channel.

The plant is the invention of Paul Shishkoff, formerly a Russian subject. It includes a novel method of storing the excess power produced at low tide so that a continuous supply of energy can be obtained at all times. The capacity of the installation is 300 hundred horsepowers.

Water for operating an ordinary turbine is caught within a dock at high tide. Then, as the tide recedes, the water is allowed to run out of the dock through a vertical pipe at the foot of which is the turbine, or water wheel. This wheel is connected by a vertical shaft to an alternating-current generator.

A working difference of level between the inside and outside of the dock of from 7 feet at high tide to 32 feet a low tide is thus made available. The plant is so designed that when this working head of water is at its greatest, more power is produced than the generator can take care of.

ORDINARY DECAY OF TEETH IS CONTROLLED BY PROPER DIET

Dental caries, a disease in which the teeth decay and cavities form, can be controlled by suitable diet, it appears from the report to the American Dental Association of Dr. R.W. Bunting, Dr. Philip Jay, and Dr. Dorothy Hard of the University of Michigan School of Dentistry.

These investigators carried on an experiment in caries control for 1 year with three large groups of children in public schools and orphanages. The children were given a varied diet, fortified by 1 quart of milk and some green vegetables and fruit for each child every day. They were given neither cod liver oil nor viosterol. They had no sugar on cereals or in beverages, very little sweetened preserves and pastries, and little or no candy.

The elimination of sugar was made on the assumption that the average child consumes more carbohydrate in this form than is required and that such overconsumption of sugar perverts the appetite for other necessary food factors, thus unbalancing the diet, the investigators reported.

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