The daily morning journal and courier., 1897-09-06
pHoroGRApHrNa THE SKIES.


 the Weather Bureau-Pictures of At mospheric Currents on Dry Plates Importance of the Expected Results | The Mystery of the Tornado May be | Solved.
 The Weather Bureau is about to en- ter upon a wholly new branch of scien- tihc investigation, namely, the photo- graphing of the air. Results are eX- pected from it of the utmost impor- tance to meteorology, throwing light upon many phenomena which at pres ent are not understood. For 1t is fact that almost nothing is known about the way in which the currents of the at- mosphere move, and it is easily seen what an important bearing this ques- ton must have upon the problems which the government forecasters are obliged to tackle. Take an ordinary hurricane, for example, such as is apt to run up the Atlantic coast from the West Indies at about this time of year. The nature of the disturbance is com prehended in a general way, but the working mechanism of the storm is mystery. A whirling tornado plucks chicken clean, drives a scantling i through man, strips a woman naked and carries a baby mile unhurt. How does it do these things? Nobody can say.
 The Weather Bureau is going to find out all about such things by photo graphing the air currents and studying their movements as shown by the ca mera. For instance, the experts want to know how the air flows over houses, over mountains through bridges, etc. They will make a little model of a mountain, place 1t before the camera, and direct an imitation breeze against it. When the wind strikes real moun- tain it flows up the slope; that much is known But what does it do when it reaches the top? Does it continue to ascend, or where does 1t get to? No body knows
 On bad days, however, the most per rect lens was apt to appear streaky when subjected to this optical test, and it was found that the phenomenon was due to warm and cold currents of air moving over the glass. This was a se- rious annoyance to the ens-makers, but some years later 1t struck another scientific man named Toepler that the trouble could be turned to profitable &C., count for the study of motions of air currents. He did something at it, but the important work in this line has been accomplished recently by Profes- sor Mach, who has made great num- Der of photographs of air moving around objects of all kinds His photo- graphs of flying cannon balls, for ex- ample, have caused certain modified tions in the ordnance employed in the Austrian artillery.
 It would seem to be an extremely diff ficult matter to photograph so tenuous and transparent substance as air. However, there is a way of doing it which has been worked out recently by an Austrian scientist, Professor E.. Mach of Vienna The discovery is de- rived originally from the experiments of two Frenchmen, Foucault and Fig eau, who invented method of produc- ing perfect lenses. They found that if a bright point of light were placed a considerable distance behind the lens, the latter from the front would appear to be illuminated uniformly throughout. If there was any imperfection in the shape of the glass it would be shown by an irregularity of coloring. In such case the spot was marked and correct ed.
 Professor Cleveland Abbe showed your correspondent yesterday a photo- graph of flying bullet made by Pro- lessor Mach. It was on piece of translucent gelatine, which had to be held between the eye and the light for observation. Not only was the con- pression of the air in fronttof the bullet clearly visible as a dark spot, but one could see the waves of air moving away from the sides of the projectile and the atmosphere rushing in behind the latter to fill up the vacuum made by its pas sage A photograph of conical can non shot had an appearance somewhat similar Professor Mach has been studying the way in which the air af- fects the trajectory or mortar shells and other kinds of projectiles, the re- suits being most useful to the Austrian artillerists
 The method by which the photo- graphs are taken is quite simple There is a large and very perfect lens, at some distance behind which are two electrodes so placed that an electric spark can be made to flash between them. In front of the lens is the came ra. Avoiding details, it is sufficient to say that the passage of a bullet behind the lens causes spark to fly between the two electrodes, and the result is g. photograph of the spark deformed by the disturbed air around the projectie Thus is produced a picture of the bull let and the atmospheric waves sur rounding it. The same process is ap- piled with other objects. In some cases the latter are stationary, being placed behind the lens and exposed to an arti- ficial breeze. Professor Mach has done this sort of thing with the wings of birds, blowing current of air against them. The resulting photograp phs show that the resistance of the air is utilized by a bird with the utmost economy of energy, none of it being wasted
 Following this method, the Weather Bureau experts will set up a little mod el of a building and blow against it with an imitation wind photographing the air currents as they move around it. At present nobody knows in what man. ner air in motion flows around a house. People often write to the Weather Bu- reau asking how strong they ought to make certain structure, as bridge, for example They want to know how to calculate the pressure per square foot of high wins. The experts are unable to furnish the required informa- tion No way of ba ,,raS-