by pressing his fingers on to it and then on a special paper form, leaves his fingerprints clearly.
These prints, together with a photograph and description of the man are filed away with thousands of others at the Yard.
Checking fingerprints with those in the bureau is a skilled business. The collections are classified by means of numbers given after an examination of the prints with a magnifying glass.
It is plain, therefore, that if the prisoner has been caught before, his fingerprints are at Scotland Yard together with his photograph and full description, then as most of the haunts of criminals are well-known to the police, it is generally an easy matter to collect the " wanted " man.
S. REYNOLDS.
TALKING FILMS.
Talking films, or as they are more commonly called, "talkies" have become very popular in this country, as can be seen by the number of picture-houses who are equipping themselves with talkie apparatus; America, the home of sound films, is making big improvements in talkies; they have even used them to record and to photograph the confessions of criminals.
However, let us consider the process by which, talkies are made. Firstly, we will review the British system, which is very different to the American method. In the British system the sound record is photographed on to a film, which is synchronized with the film running through the camera. The recording apparatus consists of an electric lamp generating a powerful ultra-violet light, which is focussed on to a mirror; the mirror vibrates in sympathy with the fluctuations of the microphone diaphragm, the beam of light from the mirror is recorded on the moving film as a wavy line. When both films are developed they are printed on one film, the sound record running on one side of film, several inches behind the actual picture it goes with, because the sound reproducer cannot be level with the projector, owing to mechanism already there. The important factor in the sound reproducer is the photo electric cell (described in the last issue in the article on "Television"), it acts in the opposite way to the recorder, the wavy lines causing the light which falls on the cell to waver and alter the resistance of the cell, which controls the current flowing to the amplifiers. The American system consists of huge gramophone records which are synchronized with the film, that is the reason why it is possible to make some scenes in silent films, into sound scenes; such as people cheering, and car racing.
FREDERIC W. WALKLING.
EUREKA.
The Authentic Version.
Hiero, king of Syracuse, instructed Archimedes to test the genuineness of his crown. The idea of determining its specific gravity is said, to have occurred to him while taking a bath and the novelty of the idea caused him to dash through the streets shouting " Eureka," (I have found it.) Who knows whether the following is not the correct version?
In the year Umpteen B.C., lived Prof. Archie Medes, B.Sc, of 13, Comic Sections, Avingyou, Syracuse. One day, on account of his being a pal of Euclid, Aristotle, Pythagoras, Sanatogen, Thermogene and other members of the underworld, he was summoned before king Hiero who had just received his crown back from the dyers and cleaners after its annual spring-clean.
Hiero explained carefully that the crown was not bought at Woolworth's, but had been delivered in a plain van at the palace for £1 down and 15/- per month, but all the same he was suspicious that someone had been exchanging- the gold crown for a cheap gilt affair. The professor was accordingly to discover immediately - if not sooner - whether it was A. 1. at Lloyd's or merely a mass-production article. Although of Scotch descent he paid the professor's taxi-fare and sent him home to test it.
Now Mrs. Archie Medes had insisted that if the professor wanted to monkey about with experiments he must take them to the bathroom. Furthermore, dinner was nearly ready and he must go and have a bath if even she was going to speak to him again ! So there !
The professor meekly hung the crown on a convenient nail, filled the bath and disrobed pondering deeply, unaware that Archie Med.es, junior, had been blowing: bubbles and left the soap conveniently on the floor.
Wrapt only in thought and a bath towel, the professor stepped neatly on the soap and plunged speedily and head