BURGLAR-PROOF GLASS.

Taranaki Daily News, Volume LII, Issue 377, 30 April 1910, Page 9

BURGLAR-PROOF GLASS.

iltiW .lIOUT.LLERS ARE I'MOTI-XT--ING THEIR WARES. if the French ivjiitiiuie their present experiments to the logical conclusion we shall perhaps one day be able to live ill glass hou»es and throw as many stones as we like.

The idea originated in .Marseilles. One day, a little more than a year ago, there war, an apparently organised imu.m-ur. of burglary in some of the principal streets V that city. In'broad daylight, and in crowded thoroughfares, the windows of more than a dozen jewellery shops were smashed ami objects of great value were successfully made away with.

.M. Maurice Nngtie, a mirror-maker of Marseilles, got the notion that glass might be made suliiciciUly 'hard and thick to withstand any ordinary attack by burglars. There wen! two ways to do it; one was to make the glass thick and tough; the other to imbed wire mesh in it, as in the front of motors. Experiments were made iii the composition of tough slabs of glass of a thickness varying from fifteen to twenty millimetres and of a clear transparency. Then tests were made of the resistance of glass under such conditions as those of the episode in Marseilles. First a pane of ordinary plate glass was struck with an iron-capped mallet, hurled from a distance of three yards. A great hole was made in the glass, sullicient, had the pane been in a shop-window, to have enable a thief to plunder the window. The experiment was then repeated with a slab of "burglar-proof" glass. This "dalle polie" was twenty millimetres in thickness. It was set in a window of ordinary shop size, but was framed in iron instead of the ordinary window sash of wood. The iron-capped mallet made no impression on the glass when thrown at it from a distance of first, three and then six yards. After that a disc of iron weighing ten pounds was hurled at the window, but this, at the lesser distance, had no other effect than a very slight bruise or abrasion on the surface of the "dalle polie," but when the distance was increased a round hole was made in the glass; but this hole was only two centimetres in diameter on the surface of the glass. It did not extend clear through the pane, and there were no radiating fractures such as usually are seen when window glass is broken. The final test was made with an army revolver, but the glass stopped the bullets when they had penetrated to the depth of one-quarter of a centimetre. The latest results of experiments is a window glass varying in thickness, and having embedded in it a very light wire running in parallel, transverse lines about one inch apart. These lines of wire constitute, in effect, one continuous line starting from an upper corner of the pane, and running from left to right and right to left across the window without a break. The wire is connected with a battery and carries always a small charge of electricity. It is connected at one of the lower corners with a magnet. If the window is broken, and the wire with the glass, the electric current is broken, the magnet is released, and by that action an alarm bell is set ringing. This hell may be placed anywhere within the house to rouse the occupants, or high up on the outer wall to summon the police or j frighten the burglar away. As it would j be impossible for a burglar to put even a hand through the glass without breaking the wire, and as the glass with its wire enforcement is very difficult to break, this product is regarded as more practical even than the very thick "dalle polie."