THE UPPER AIR

Lake Wakatip Mail, Issue 4008, 14 July 1931, Page 7

THE UPPER AIR

USE OF ROCKET IN METEOROLOGY Experiments with rockets, to which are attached instruments lor measuring temperature and density of the rarefied upper atmosphere, have attracted widespread attention in recent months. Some reports fancifully suggested the possibilities of journeying to the moon, but the immediate object is to extend meteorological observation, and even from this standpoint only partial and limited success has so far been achieved. Describing in the 1 Manchester Guardian : the nature and object of the experiments, Dr Darwin U. Lyon states that the density of the atmosphere decreases roughly by one-half with each and every three miles of ascent. Airmen at seven miles and above have encountered temperatures as low as Codeg below zero, and sounding balloons have brought back temperatures olH2Udeg at a height of. eleven miles. 1' roin here on, however, our knowledge is very uncertain. At sea level and up to heights of seven or eight miles the atmosphere consists of 78 per cent, nitrogen, 21 per cent, oxygen, and about 1 per cent, argon. There was reason to believe that at heights beyond this the percentage of oxygen decreases while the percentage of nitrogen increases, and it would appear that at a height of about forty miles nitrogen comprises over 90 per cent, of the atmosphere, such as it is, while oxygen has lallen to less than 7 per cent.' At such a height the atmosphere is attenuated to less than one-fifteenth-thousandth of its density at sea level. Even at a height of nineteen miles more than 99 per cent, of the atmosphere is below that level, its density is but one-hundredth of that at se:i level, and proportion of nitrogen has risen from 78 to 87 per cent. But all these figures are based on theory awaiting verification. The building, handling, and firing ol rockets, Dr Lyon adds, is difficult and dangerous work. Of six large rockets constructed in the last four years one exploded while still in the workshop, three at or near the start, and only two succeeded in getting away from the earth to a “ successful ’’ height. The smaller of these carried no instruments, and barely climbed to 3.00011; the larger, over Bl't long, carried apparatus for recording atmospheric pressure and temperature ami for obtaining a sample of the upper air. This rocket was fired on January 29, 1929, and reached a height of 5.9 miles, at which the density of the air was 212min (compared with 700 at sea level) ; temperature 18deg below zero (Fahrenheit), and the composition almost exactly the same as that found at sea level. The persistence ot oxygen in normal proportions at this level (if theories are correct oxygen should disappear at fifty miles) Dr Lyon ascribes to the influence of the troposphere, reaching up six and a-hall to seven miles, in which all clouds and other phenomena known as “ the weather ” occur. Above this troposphere the stratosphere extends upwards for forty-five miles, and it is here, according to theory, that the percentage of oxygen decreases and nitrogen increases.

LARGE ROCKET EXPLODES

This year an attempt was made to discharge a rocket 12ft long and weigh* mo- with apparatus and instruments, 1321b It was so constructed that as soon as one section had finished its work the empty shell would drop oit and automatically ignite the charges in the succeeding section. A parachute to which the recording instruments were attached, and a 7in gryoscope, to keep the rocket “ true ” to its course, were added. This 1931 rocket was, as ;ar as Dr Lyon knew, the largest ever constructed. To lire it the laying of rails up the side of a mountain, gradually curving upward till they ran only I Defer or 15deg from the vertical, was planned. This method was given up on account of its cost, and recourse made to skis. By means of special mechanism II was hoped that once the rocket had acquired a certain velocity it would leave the ski carriage and continue us journey into space—hold from deviating from its course by the revolving gyroscope within. In the preliminary trials, using hut a few ounces of explosive, the method was found to work fairly well. Only three days before the date was set for the actual firing the locket was tried out on a slightly steeper slope, and with a larger supply of explosive. The rocket had travelled but a few yards when it was seen to be slipping sideways, and one of the mechanics endeavoured to push it into the right direction with a pole. The pressure brought to bear on the axis of the gyroscope loosened it from its hearings and it fell downwards through the rocket, with the result that the entire charge exploded at once, killing one man and seriously injuring two others. STARS BETTER KNOWN.

Dr Lyon’s account of his own experiments was brought to the notice ol tin* Acting Commonwealth Meteorologist, Mr W. S. Watt, who observed as a curious fact that our knowledge of the remote stars in time and extent, should be so much in advance of our knowledge of the upper atmosphere (states the ‘ Melbourne Ago ’). Only the last few decades had witnessed sufficient observations by manned and free balloons carrying self-registering instruments to fill in a picture of the kind of atmosphere which stretches up to the twelve-mile limit. Beyond fifteen miles, Mr Watt added, there are practical limitations in the way of cost and techideal difficulties in extending observations. Above this frontier limit of observational knowledge, man’s mind by scientific calculation and inlcrence has predicted the characteristics of the higher atmosphere. J his pieicing of the veil by the theorists has been a challenge and an appeal to the ingenuity of the experimentalists to provide means of actually measuring the properties of the highest atmosphere so as to check the predictions. Here it is that the rocket has come to the rescue. Outside the earth is another but invisible boundary surface about nine miles high over the, Equator and live miles high over the Poles, called tropopause. Below this surface lies the troposphere, in which the air has much the same composition throughout, clue to vigorous vertical mixing, and in which the temperature falls on the average about 3deg Fahrenheit per I,oooft. Experiments made by the Commonwealth Meteorological Bureau some years back indicated that the height' of the tropopause above Melbourne was about six miles, and the temperature about —90deg Fahrenheit The actual records were made on a

piece of metal no bigger than a postage stamp. Above the tropopause lies the stratosphere, in which the temperature ceases to fall, and until recently it was thought that the temperature was constant in a vertical direction, although it was known to vary horizontally. Paradoxically enough, the coldest air over the earth (130deg Fahrenheit) lies over the Equator DOES UPPER AIR TEMPERATURE RISE? Professor Goddard, of America, and, as mentioned earlier in this article, Dr Lyon, of England, are now experimenting with rockets. It used to be thought that above the tropopause temperature remained constant, but now theorists have predicted from observations from meteors and sound explosions that the air temperature begins to rise again about twenty miles height, and reaches a temperature equal to the ground at a height of twenty-seven miles, while it continues to rise to heights of at least thirty-six miles. The rockets will test this, and, if incorrect, enable the theories to be revised. The luminosity of a meteorite is caused by great heating by compression of the cap of air in front" of the projectile, causing the meteorite to incandesce and evaporate. Now the initial temperature or this air can be calculated in terms of observed and known quantities, and thus it is that the scientists Lindemann and Dobson have in recent years indicated the presence of relatively high temperatures in the higher layers. Sources of intense sound have been found to be surrounded by alternate zones of audibility and silence, and theory indicates from these sound observations a rise of temperature in the upper air from twentv to at least thirty-six miles.

Another fascinating problem is the composition of the upper atmosphere. Below the tropopanse convection maintains a constant composition, above it other factors determine the relative amounts of the different atmospheric elements, nitrogen, oxygen, and the small quantities of other gases, the lightest of which are hydrogen and helium. Mathematical physicists have worked out that up to a height of 120 miles nitrogen is the predominate gas, and that above that the light gas helium preponderates up to the very limits of the atmosphere. Up to the present no direct samples of air in the highest layers have been obtained, and it "may be hoped that rockets will soon supply this want.