SCIENCE NOTES.

Digger (Invercargill RSA), Issue 41, 24 December 1920, Page 13

SCIENCE NOTES.

RAPID PHOTOGRAPHY. One second is a brief period of time, and if we concentrate our attention on such a period, and then try to imagine the taking of 15,000 separate successive photographs during that time, the feat will appear to most of us absurd and impossible. However, there appears to be no limit to the ingenuity of man. Provided that a definite problem is set, and attacked by properly trained roen, with facilities for experiment and research, a successful solution may sooner or later be confidently anticipated. It is so with rapid photography. It was about 40 years ago that the use of certain "rapid" photographic plates made it possible, for the first time, to ob. tain a photograph of a cannon ball in fiight. Certainly all that could be seen was 'a black, smudgy line, marking the path of the pi'ojectile, but the achievement was regarded by man as something distinctly in advance of previous efforts. Later ; an Englishman further perfected apparatus and plates and obtained a distinct piciure of the projectile during its fiight. Then came the idea of a series of rapid pictur,es, and scientists saw at once the value of this for noting matters that were too rapid for the eye to see, such as the wing movement in a fiight of birds, insects, etc. One experimenier, working on the fiight of pigeons, perfected apparatus that enabled him to take 12 photographs a second. To-day ordinary moving picture photographs are taken at the raie of 250 per second, though about 15 a second is said to be the most generally useful gpeed. A Frenchman, M. Bull, first succeeded. in taking 3,000 pictures a second, a-nd has followed up this success, using a process invented by a fellow-country-man, by taking 15,000 photographs per second. Only a limited. variety of things can be so photographed : the passage of a rifle bullet, for instance. It is, of course, impossible to conceive of a camera shutter that could open and close 15,000 t-imes a second. This difficulty is overcome by using the electric spark. Each spark lasts a fe-vy millionths of a second, and thus the necessary rapidity and illumination are obtained together. l..e travelling bullet pas-ses in front cf the spark and its "shadow" is projected on to a moving film ; the "photographs" so obtained are quite clear cut and definite. The apparatus is arranged so that the firing of the gun sets the whole thing in motion, and the bullet, as it passes away, cuts certain threads and thus stops the apparatus. One of the workers, M. Abraham, has still further perfected the control of the sparking apparatus, and contemplates the possibility of taking similar pictures at the enormous rapidity of 80,000 a second. THE LAZIEST OF ELEMENTS. Chemically active elements are those which, like oxygen or chlorine, are anxious to comhin.e with other elements. There are a few elements classified as lazy or inert, desiring as it were to be left alone, and entering into eombination with other elements only under special and rare eonditions. The nitroge-n of the air has such ! characters, but modern chemistry has sbown several other gases even mere inert. Of these the chief is the gas Argon ; this gas forms one per cent. of the atmosphere, and was discovered by Sir Willia-m Ramsay, about 1894. It has been noted that when nitrogen was obtained from the air it was heavier than nitrogen obtained by chemical means from various compounds ; this puzzling feature was not under stood until it became known that atmospheric nitrogen was accompanied by the gas argon, as well as by minute amount-s of other rare gases. Even when argon became known, it was regarded as a useless asset as far as man's industrial activities were concerned. Now, however, the ver^inertness that caused it to be regarded as valueless is found to be the character that renders it valuable. Not many years ago our electric light bulbs were made to enclosc a vacuuna Dr Irving Langmuir, in that great wonderland of recent discovery, the research laboratories of tlie General Electric Company, UnS.A., discovered that it was an advantage to fill the bulbs with argon. The metailic filament in these bulbs is made of another equally wonderful element, the metal tungscen, only recently

found to be valuable, and for which new and important uses are continually being discovered. By filling the bulhk with 90 per cent. argon, the heat from the filament is less readily conducted away, the evaporation of the metailic filament is decreased,^ind thus a much higher efficiency and the construction of more powerful lamps is made possible.