Science Siftings

New Zealand Tablet, Volume XXXIII, Issue 52, 28 December 1905, Page 29

Science Siftings

By • Volt '

Liquid Air. The production of liquid air is thus outlined : Air is compressed to 1200 to 1500 pounds per square inch ; passed into receptacles where it is freed from moisture and other impurities; then , into expansion chambers and through long coils of pipe. It becomes intensely cold, reaching finally 312 degrees below zero, at which point it becomes liquid. The liquid is drawn off into insulated vessels, and keeps for days, gradually lessening until is is all evaporated. A New Mirror. An invention which will interest women is a mirror arranged with three supporting arms fastened at the rear of the mirror. Two of these arms fasten over the ears, and the third is attached to the chest of the user. With the mirror so fixed the user has the command of both hands, and when with her back to another mirror, is able to see and arrange her back hair, adjust the back of a dress, and accomplish many other necessary ' feats ' without the help of a maid. Number of Papers. A statistician has learned that the annual aggregation oi the circulation ot the papers of the world is estimated to be 12,000,000,000 copies. To grasp the idea of this magnitude we may state that it would cover no iewer than 10,450 square miles of surface ; that it is printed on 7*81,250 tons ot paper ; and, further, that it the number (12,000,000,000) represented, instead of copies, seconds, it would take more than 33a years for them to elapse. In lieu of this arrangement we might press and pile them vertically upward to gradually reach our highest mountains. Topping all these, and even the highest Alps, the pile would reach the magnificent altitude of 490, or in round numbers 500 miles. Calculating that the average man spends hve minutes in me day reading His paper (this is a very low estimate), we find tha* the people of the world altogether annually occupy time equivalent to 100,000 years reading the papers. • The Art of Daguerre. Although the improvements in photography are made so rapidly nowadays that even the piotessional photographer can hardly keep track of them, there are many picture-makers (says the ' Century Magazine '), who belie\e the world will turn back to the daguerreotype for its beautiful and most artistic portraits. It is more than sixty years since the scientific world was aroused by the announcement that Daguerre, a Frenchman, had discovered a method of fixing the image made by the camera obscura. It was a crude method then. The first picture, of a tree standing in the sun, lequired half an hour or more of exposure. That was tiie same year in which Samuel F. B. Morse went to Europe to exhibit his new electric telegraph. The two inventors met by appointment in Pans and explained thefr work to each other. Daguerre's plate was of pure silver. It was thoroughly cleaned and polished. In a dark room it was next coated with a film deposited by the vapour of iodine, and then exposed to the camera. Still protected irom the light, it was placed over the fumes of hot mercury, wnich developed the image, and it waai then made permanent with chloride of gold. This process was soon improved, until on bright days the sitting for a daguerreotype was reduced to ten, sometimes to five, minutes. Even with this short exposure, however, the likenesses were remarkable. It is possible to assume an artificial expression and hold it lor a brief second betore a modern camera, but to remain motionless for the long time required for a daguerreotype, it was necessary that the features should be in repose in their natural position. The daguerreotype was a positive, impossible to retouch. It was a soft, flesh-like tone, which even today, in the specimens of the art preserved in collections and among family relics, wins admiration, The daguerreotype gave way to the cheaper arnbrotype, which was on glass, and required a dark background to show it ofl ; and this in turn was succeeded by the glass negative and the paper positive print. None of them has ever attained the delicacy or the softness of the daguerreotype, and the P'renchman's method, expensive and slow as it is, may win its way back into the popularity it bad more than half a century ago.