ASTRONOMICAL NOTES.

Press, Volume LXIV, Issue 19482, 1 December 1928, Page 11

ASTRONOMICAL NOTES.

FOR DECEMBER, 1928.

(SFECIAIiLT WF.ITTEN- FOR THE PBESE.)

[By E. G. Hogg, M.A., F.E.A.S.]

The sun will enter the zodiacal sign Capricornus on December 22nd, when the solstice occurs; this will be the longest day of the year in the Southern t Hemisphere, the sun being above the horizon for 15 hours 27 minutes. The meridian altitude of the sua will be 69deg. 56min for the latitude of Christchurch and the distance of the earth from the sun will be about 91,-170,000 miles. The planet Mercury rises on December Ist at 4.20 a.m.; it is approaching the sun, with which body it will be in superior conjunction on December 18th; towards the close of the month it will set about half an hour after the sun, well to the south of west. Venus sets on December Ist at 10.48 p.m. and on December 15th at 10.49 p.m. Mars rises on December Ist at 10.11 p.m. and on December 15th at 8.58 p.m. Jupiter rises on these dates at 4.28 p.m. and 3.29 p.m. respectively. Saturn sets on December- Ist at 8.37 p.m.; it will be in conjunction with the sun on December 13th when its distance from the earth will be about 1025 million miles; it will become visible in the eastern sty towards the end of the month. An occultation of the planet Mars by the moon, visible in Christehurch, will occur on December 26th; the planet and moon will rise close together on that day at 7.48 p.m. and will be in a line with the earth at 8.30 p.m. Mars will be in opposition with the sun on December 21st, when its apparent magnitude will be—l-4 or only one-fifth of a magnitude fainter than Sirius. It will be at its least distance from the earth on December 15th, when the two bodies will be about 54,400,000 miles apart. Cosmic Rays. It is only of recent years that we have come to realise the important part played by radiation in the realm of physics. A century and a quarter ago the' undulatory theory of light was placed on a satisfactory basis by Young, Fresnel, and others, when it passed into common knowledge that light and heat are propagated by waves tlirough an etherial medium at the rate of lab,OU miles a second; in 1887 Hertz was con-: ducting the experiments which led to the detection of the electro-magnetic waves which are now used in broadcasting- X-rays have only been known to us since 1895 while the Gamma-rays emitted by radio-action substances are a still later addition to our knowledge. These wave-groups are allsimilar kind and travel through the ether at j the same speed, but they differ enormously inter se in their wave-lengths and physical properties. Recent researches have brought to light the existence of still another waveeroup and . its name—cosmic ' rays—is sufficiently indicative of its suspected origin to warrant us in devoting some time to it in a column concerned with astronomical matters. The evidence for the existence of this cosmic radiation will be placed before our readers m its historical order as this procedure will, in the words of Professor R. A. Millikan, to whom much of our knowledge on the subject is due, have the further advantage of P res ® a beautiful illustration of the slow, step by-step process by which most advances in science are made, each experimenter building on the past, but pushing on, if he is fortunate, a little heyondwto his predecessors had ; gone, L n sently the world finds itself ,in ? the full glory of a new conception of Nature Without having been conscious of any. particular instant at wh fV r ® mv* came. , Since the days .of Greek my tholocv* very few discoveries t sprung full-grown out of the brain of anyone." , Early Experiments. As -we shall frequently refer to an taSit «*a i» *££ ■i/k "poqmic rays, called an eiecui TZ, ipWa tkrt.m rt.. s.m£ lest form it consists of an insulateQ conductor to which is attaehed a pai of thin sheets of tinfoil or gold-leat, if a charge of electricity is given to the conductor, the leaves are repelled from each other and their divergence is a rough measure of the amount of the charge present; the approach of the leaves to each other is evidence of a diminution of the quantity o electricity on the conductor and when the electroscope is discharged oi-de-prived of its free electricity the leaves collapse and hang vertically. It had been observed that a properly insulated electroscope, if left to itselt, slowly lost its charge and it was suspected that .radiation in some form might be the cause as it had been discovered that if an electroscope was exposed to radiations from a radioactive body it became ' discharged. Working on this idea Rutherford, McLennan, and others found m 1903 that' the rate of discharge of an electroscope could Ibe very markedly reduced, by surrounding it by protective screens of lead several centimetres thick, thus showing that rays existed in the atmosphere capable of passing through a considerable thickness of metal and these rays became ■ known as penetrating rays: it was thought at the time that they were in some Way connected with other radio-active phenomena. In 1910 the Swiss _ physicist Gockel took an electroscope in a balloon to a height of 4500 metres and found, contrary to expectation that the rate of discharge of his electroscope was higher at this' altitude than at the earth's surface, a fact which at once suggested that the radiations concerned were not all of terrestrial origin but that part came into the earth's atmosphere from above. These observations were tested , in other balloon ascents, in particular Kolhorstef taking balloon readings up to 9000 metres found that the radiation was seven times as strong as at sealevel. Millikan and Bowen in 1922 sent up recording electroscopes to a height of nearly 10 miles and obtained results which showed that if the radiations came from the higher parts of the earth's atmosphere they were more , penetrating than, had been supposed ' up to that time. ' Though it was sug- ' gested that the radiations came into the earth's atmosphere from outside, i.e.. were of cosmic origin, it was far from being proved that such was the case, and it "may be said that in 1925 many physicists were ot, opinion that this' interpretation of the observed i phenomena could not be maintained. Eecent Work. | The further investigation of the I origin of these rays in 1925 led to evi- ' dence which pointed without doubt to their cosmic origin. Millikan and Cameron prepared a special form of electroscope, which was very sensitive, and this was sunk into the waters of deep, high-alitude, snow-fed lakes. At Lake i Muir (altitude 11,800 feet) the instrument had to be lowered 60 feet into I the water before the action of the rays | to affect it, i.e., a screen of | water 60 feet thick was required to cut off these penetrating rays. They next sank the electroscope into a lake 300 miles further south, and having an i a ititude of 6700 feet, and here they obtained a series of rqpults very similar to those of Lake Muir, but with each reading displaced six tfeet up- '