From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article discussing the scientific technique of photographing invisible phenomena like sound waves and air currents.
| Identifier | ExFiles\Box 143\3\ scan0190 | |
| Date | 25th April 1940 guessed | |
| 16 1204 PHOTOGRAPHING THE INVISIBLE As beer is poured into a glass, carbonic acid vapor overflows. Normally unseen, the phenomenon is visible in this picture. The camera sees more than you do. It records physical phenomena such as sound waves and air currents which the eye normally cannot observe. By J.{Mr Johnson W.M.} H.{Arthur M. Hanbury - Head Complaints} W. KERSTON HAVE you ever seen a sound wave? Do you know how hot air looks as it rises from a source of heat? Or vapor rising over a can of volatile liquid? We are constantly surrounded by such physical phenomena which take place before our very eyes, but which are invisible to the eye. Science, however, has not been content to let matters rest there. Brilliant physicists, applying certain optical principles, devised a means of making these phenomena visible, not only to the eye, but to the photographic film. Now it is possible to make beautiful and striking pictures of a bullet in flight showing the sound waves it makes as it travels at top speed. We can photograph sound which emanates from a point source and travels in all directions, much like the waves formed by tossing a pebble into a pond of still water. Other forms of waves generated by vapor and hot air, and which are normally invisible, can be made visible and recorded on film. The technique of this process was discovered in 1864 by the eminent scientist Toepler. However, it is only in recent years that it has been practically applied in every conceivable branch of industry and science. The accompanying illustrations show a number of photographs of ordinarily invisible phenomena in the fields of acoustics, ballistics, flow-physics, and heating. It is difficult for the average person to identify the subjects shown in these interesting pictures. Try it on your friends, but cover up the captions first. You'll have a lot of fun. The development of this highly specialized branch of photography has advanced to a remarkable degree. While methods differ slightly, that developed by Toepler is of great value compared with others because it does not affect the phenomena themselves, and with it one can now, in some cases, make quantitative measurements for scientific purposes. Thus technologists throughout the world are at present engaged in applying photography of the invisible to their own peculiar problems. It is not impossible for the amateur to experiment in this same field himself as will be seen later. But first let us examine the principles upon which this fascinating subject is based. Do you remember standing at a railroad crossing on a fine, hot summer day and looking down the tracks as far as your eyes could see? Do you also remember that the rails seemed to wriggle under the scorching sun? Or do you remember looking through a window pane of uneven glass, at a telephone pole or chimney that seemed to be bent? We all know that a beam of light, passing from an optically denser medium to a thinner one (or vice versa), is deflected from its straight path or refracted. This phenomenon is also strikingly demon- (Continued on page 74) | ||