ASTRONOMICAL NOTES FOR JUNE.

Press, Volume L, Issue 149814, 30 May 1914, Page 8

ASTRONOMICAL NOTES FOR JUNE.

(Bt thx Rev. P. V. Faibcxoxtgh

F.R.A.S.)

[Mercury is an evening star, but, like Saturn, is difficult to find in the glow of tho sunset. Venus is becoming an easier object. She will be occulted by tho moon at about 7.30 p.m. on tho evening of the 26th —too late for New Zealanders to see it. Jupiter is also a late evening star. Ho rises in rare splendour about 11 p.m., and is probably making some people imagine they see tho head light of an airship. But if Jupiter were coming at us with a speed of 10-t miles an hour, which would be a good average for an airship, he would bo considerably more than four centuries on the journey. Mars is now inconspicuous, and is situated west of Leo.

Orion is now to be seen only early in the evening. The Twins also disappear early. Leo (the Sickle) is also working westward. Lyra, with tho flashing Vega, is in the north about midnight. Arcturus is the finest star to tho northward. Spica, in tho Virgin, is nearly overhead. Scorpio is in tho east in the early evening. The red star Antarcs, or the false Mara, is tho Scorpion's heart. In the north is also seen a circlet of stars, the Northern Crown.

Lowell, after a long 6tudy of Saturn's moons, announces that two of them, Tethys and Dione, vary in their light about one quarter of a magnitude, and that tho period of the variation is coincident with that of their revolution round the planet. This means that theso moons, like our own, turn one face to the primary all the time. In the course of a revolution all sides are turned to us, but for some reason one side is a better reflector of the sun's light than tho other.

Lowell claims to 6ee the Canals of Mars with his new 40in. reflector es "fine direct geometrical lines." Ho considers this a triumph for his theory; for it had been prophesied that better instruments would confute the canal theory by showing that there was nothing of the naturo of such markings on Mars at all.

The question whether light is absorbed in space or not has been attacked by a. new method. It is known that light shining through fog or dust loses its violet rays -first, causing the light to appear red. The atmosphere is blue because of blue rays captured from light passing through it. To apply this principle, pairs of stars with similar spectra, bnt known to be at different distances were - v compared. It was found in the majority of cases that the more distant star was weaker in violet than the nearer.

So greatly have instruments been improved that it is possible now to measure the hundredth part of a second of arc with as much accuracy as a tenth could be measured thirty years ago. Hence all new measures of the distance of stars are much more reliable than those of a generation ago. In order to realise the fineness of this measurement, let us take an example. A threepenny piece hold at arm's length will eclipse the moon—to one eye, of course. The moon is 1860 seconds across. The hundredth of a second is the angle subtended by the 186,000 th of the moon's apparent diameter, or of the little coin at arm's length.

A detonating fireball passed over Reading, Oxford, and other places in England on January 19th, giving more light than the full moon. Its motion was slow—only about twelve miles per second, and as it was seen for six seconds, its visible path was more than seventy miles Jong. Tho path sloped from fifty-one miles high, when first seen, to eleven miles when last recorded. •No doubt it fell to earth somewhere, but no one saw it. Its detonations wero like distant artillery, and flashes, or explosions, preceded the sounds by intervals dependent on the height above the earth. January has been rich in fireballs for years past; a fact that seems to indicate that in that month we cross a stream of large meteors.

Some time ago we described Professor Joly's attempt to ascertain the age of the earth by means of tho amount of salt in the sea. All rain is without sodium, yet all rivers contain sodium, and are carrying it to tho sea. Hence the everlasting circulation between the sea and the rainfall is a process of bringing salt down to the soa and leaving it there. How long has this process been going on? 'lo answer this question, a number of facts require to bo known, such as tiie volume of water in the ocean; its average salinity; the annual output of the rivers of tne world, and the percentage or salt contained in that output. .Having ascertained the safest estimates of tiiese factors jn tho problem, or the average of them, the matter is still complicated by what is called "cyclic sodium," or tne saline matter in tho spray which is carried great distances inland by high winds. This, of course, must not be counted as part of the sea's annual increment, seeing it is only a temporary loan from the sea to tho land. Many carerul observations have, however, iairly solved the question as to the amount of cyclic sodium to be allowed for. A much more difficult problem is to allow for the amount of salt obtained by tho rivers from aqueous rocks, sandstones, chalks, and so forth, which were originaliv under the sea, and derived their salt from that is being repaid-a long-dated loan Si, c - vcbc **& » * short-dated loan. Tho enqjiry is to »find the amount ot salt taken from original igneous rocks and carried once for all to the 6ea.

Professor Joly concluded that the 97 V 6oo h OM 6 l*** & ° W i ms in u to thSS. fcj y< ,000,000 years. In the "Scientific itflTU F - W -, describes a later effort to grapple with tho problem the result being somewhat less, but jtiU strikingly similar. The saline matter of the ocean is stated at 4.800.000 8-1,300,000 cubic miles of igneous rock would require to be decomposed. The entire annual "run off" of the globe is stated at 6524 cubic miles of water which are estimated to contribute to the ocean's stock 148.046.000 tons of sodium, additional every.year after all reasonable deductions have" been made for cyclic salt, etc The time during which the rivers have run into the sea premises, is found to be 59,222.000 years—a result that differs only by about 5 per cent, from JolVs. Some new investigations as to windblown salt were then taken into account. Some scientists are of opinion that the Dead Sea owes its intense salinity to wind-blown 'salt. Lake Sambhar, in northern India, is 400 miles from the sea, but careful experiments show that no less Than 3000 tons of wind-blown 6alt fall into this small lake annually. This unexpected result tends to show that more allowance mufct l>e made for cyclic salt. A rain it has to he remembered that a large par; of the volcanic action of the tclobo takes place in the sea and that a coa-

siderable proportion of the ocean's 6alt may be derived from that source. These considerations tend to lengthen the period during which the rivers would have to run into the sea to produce its present salinity. Again, if the primeval ocean were saltish, owing to the volcanic or scoriatious nature of the surface of tho globe when the original vaporous envelope condensed into water, that too would have to.be-al-lowed for. Putting all these things_ together, Clarke arrives at an amended estimate of 99.140,000 years as the age of the earth since land and water appeared. These .figures again, are of the same order as those already quoted, which tends to strencthen our confidence in this method of judgHe the aire of tho earth. "We may add that tho honour of suggestins this line of enauiry is due to no less a person than Edmund Halley, centuries before knowledge was approximately sufficient to enable it to be followed with any hope of success. In inquiries of this nature tho quantities are so vast that what appears to be a serious factor is really negligible Thus, there are enormous salt beds ; n the world, which are part of tho sea's salt, lost for a time. Doubtless this salt was originally carried to the sen by tho rivers and should be allowed for. But when we consider the amount added to tho ocean's stock every year— about 150 million tons, wo see that a comparatively few thousand years, probnblv much loss than n million, would be sufficient to accumulate a'" the salt beds on the globe. The salt beds are therefore noelkiblo. as a fewthousand years, in such an enquiry, are neither hero nor there. In the same way tho sodium of aqueous rocks if shown not to be great enough to vitiate results. If 15 r>er cent, of th<> 83.300 000 cubic miles of the ori"inal rr»eks decomposed to procure the salt of the sea, hsTd become sandstone, and if 20 pt cent, of its volume had been pores filled with sea water, the salin<matter left in +hr> F! >»"'«*«« wouV have been 118.730.000 000.000 tons of sodium. But even this incomprehensible amount would repr<"="i f . only the lohonr of thn rivers for 750 nr>o years, which a<rnin >s almost negligible in such huge periods.