SCIENTIFIC MYSTERIES.

Dominion, Volume 3, Issue 819, 17 May 1910, Page 6

SCIENTIFIC MYSTERIES.

WILL SOON BE SOLVEDT MAY SEE A SIGHT NEVER SEEN BEFORE. Mr. Fredk. R. Fiold, of Aramoho, In a letter to The Dominion, dated May 14 gives some very interesting facts and opinions about the comet. He writes as Dominion gives notes upon Halley's comet by Father Allen of Meeance , Observatory. When he speaks of the comet's head being 79,000 miles through he. of course, includes the wholo ot the comet, not merely the nuc eus, for the latter is, apparently only about tho sizo of the earth. Though there is no record of a comet's nucleus having been visible whilst passing in front of tho sun it is highly probable that such a sight may be witnessed on this occasion-that the nucleus will be seen as a nebulous round blotch in diameter about one-twentietn that of the sun, travelling across almost tho middle of the sun from west to east. Friday morning was the first morning we have had for some time clear enough to observe the comet; but even then the air cannot have been so clear here as at Meeanee, for though the measurement of tho tail showed it long enough to reach the earth, there did not appear to bo as much as 3,000,000 miles to spare. As viewed from, the earth, the tail appeal's to be about 2,000,000 miles wide at the port where tho earth will pass through. This means that whilst wo are in the tail we shall have it extending for about a million miles north and south of us, for we pass very nearly through the middle of it. But it by no means represents the length of the earth's journey from front to back of the comet's tail. More Than 14 Hours. The timo occupied in passing through will undoubtedly be much more tiian 11 hours It is reasonable to expect that the earth will pass through the first and lHitest, jet (so to speak) of the tail at ■ibout 8 p.m. on Thursday next, through another such jet at about tho same hour or earlier on Friday, and enter tho maiu and densest portion of tho tail about Saturday afternoon, not to emerge from it entirely till' fully two days later. Thus there would bo aomo part of the comat*«

Uil between us and the sun for at least lour days alter the transit of the nucleus on Thursday afternoon. Meteorological observations must be alfected, but to wnat extent and in what direction cannot be predicted, The brilliancy und <:oloui ol inn aim may be expected to snangv. Whilst passiujj through the tail at night wo shall, probably notice souib twilight effect, more particularly bclore sunrise on Sunday. Tho pretence of the moon will render this less noticeable earlier in tho night. From now on till Thursday .the tail, seen botore sunru.e, will appear both to lengthen and to increase its spread. An Extraordinary Spectacle, Very little, 'if any, of it will be visible just after nmsot on Thursday, and, if seen clearly enough, will present the extraordinary spectacle of a comet with tho outer end of its tail turned back towards the sun. From I'riday onwards the of the tail will appear to grow less, its outline for a time appearing curved. The length will seem to incr«as<) for a time, and to be at its greatest probably on the evenings of tho iiih and 25th. Tho old notion that wo shall experience increased temperature may prove correct. But I should expect instead a slight general fall in the thermometer for the first two da-vs after the transit, then a slow rise to normal. If the solar radiant theory bo sound, the barometei. may be expected to rise several times above normal, indicating tho highest pressure about Sunday morning. But, if the theory be incorrect, there will probably bo an unusual fall each timo wo enter a section of the tad. Strong winds may be looked tot, hi ancti ways tho barometei and thermometer may help to settle various questions that are in doubt, but tho objection to them is that tho observations are not amenable to check. Electric and magnetic disturbances directly due to tho comet are not so likely to be detected. Hay Reveal Mysteries. But the most important investigation to bo made, I think, whilst the comet is passing us, lies in the direction of refraction. Observations taken to the sun before and during tho transit of the nucleus, and to the sun and stars periodically for several -days afterwards, uould probably reveal to us .some of the mysteries, not only of comets, but also of the circum-solar medium in .which our planets move. We now have an unique opportunity of making some comparison between the densities of the comet's gases and the surrounding meIf, as is generally believed, the comets tail be composed of gases in vacuo, then directly the head begins to intervene between us and the sun' the western sido of the sun must become distorted. When the comet's head, occupying about half the sun's diameter, reaches the opposite, or eastern, side of the sun that side also must appear distorted, perhaps visiblv so. This suggested distortion, which would gradually spread over the whole sun, and then make it to appear to move irregularly and slightly out of its proper course cannot, with our present knowledge, bo exactly foretold, because it must depend upon conditions which those distortions alone can tell us. The observations taken on Saturday and Sunday would probably show the irregularity at its greatest, and, if the conditions be as generally surmised, should then represent the sun considerably in advance of its calculated position. On the other hand, if the comet's tail be dependent upon gravitation, those observa-

tions will show the sun somewhat behind that position. I Valuable Scientific Data. In any case, observations taken upon the lines I suggest would in all probability throw a flood of light upon much that is now beyond our ken. A series of photographs of the sun, taken during tho transit of the comet's head on Thursday afternoon, might fairly be expected to show a sight that has never been seen before, and to yield scientific data of the greatest value. So far as I know, tho observations referred to have never been attempted before, and are not contemplated by astronomers at the present time. Such 'an opportunity as the present is not to be lost; for it cannot be expected to occur again within the next few centuries. As for the transit of the comet's head, we, on this side of tho world, shall have it all to ourselves. I wonder that the leading astronomical societies have not made more preparation for it, and I heartilv wish that our local observatory, with its very capable director, may score some distinction in the direction indicated.—l am, etc., FRANK R. FIELD. Aramoho, May 14, 1910.