WHEN WE STRIKE IT.

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

WHEN WE STRIKE IT.

CANNOT HURT US. "NEAREST THING TO NOTHING." DR. KENNEDY INTERVIEWED. Some of the questions which people are asking about the comet, and especially about the approaching contact of its tail with this planet, were put to the Rev. Dr. Kennedy by a Dominion reporter last evening. Can you tell me the exact times when we shall enter the tail and emerge from it? "It is impossible to say exactly, because the motion of the tail is somewhat irregular. Wo shall pass through it during the night of Thursday next, May 19.' Tho head, or nucleus, will transit across tho sun from 1.50 to 2.50 p.m. on Thursday, and the earth should, therefore, enter the tail early the same evening. We shall be in the tail at least 12 hours. With tho earth travelling 18.3 miles a second and the comet 2G.5 miles a second in tho opposite direction, we shall pass through at a velocity of nearly 45 miles a second, and as the thickness of the tail at that part is estimated at two millions of miles, you will see that we should be in it at least 12 hours." What part of tho earth will be tho first to enter the tail? "We cannot say, because we do not know the exact time when we shall encounter it, but within three minutes of the first contact, the whole of tho earth will be enveloped. The tail will appear to come to us from the east." If It Was the Head? What would happen if tho earth came in contact with tho head instead of tho tail? "There would .probably be a very interesting shower of meteors. Somo of them might lie large enough to reach tho surface of the earth, and might do a little damage. We do not, know the sizo of the particles in the nucleus, but some think they are only as big as pins' heads and hundreds of feet apart from each other. If they are as small as that, thoy would be vapourised and lost before reaching the surface. of the earth. It is generally thought that no harm would result, even if the earth came into contact with a comet's head." Is it definitely known what tho tail of Hallcy's comet is composed of? "It is known to bo composed of glowing gas at n very low pressure. Up to last January tho result of photographs of the spectrum was that it contained cyanogen and nitrogen, but I see now that a cable from Madrid states that tho presence of cyanogen has been disproved. Cyanogen, which is ono of the hydrocarbons, is poisonous, but as comet's tails nro so rarefied, we should have no occasion to fear anything even if tho tail of the approaching comet consisted of nothing but cyanogen. I believe that nearly all the comets' tails that have been examined with the spectroscope have been found to contain ono of. the hydro-carbons —tho group of gases which includes cyan--oSt,n' What We May See. What, shall we see as we pass through the tail? "Nothing, except perhaps a glow of light in the heaveus during the night, Jjut as the moon will bo about full at

the time, there is very little prospect of anj' unusual light of this kind being observed. There is a possibility of a number of meteors being seen, because although the tail is mostly gas there may be a lew very small particles of solid matter in it. They will be quite harmless, as they will bo turned into vapour in passing through our atmosphere. There need be no fear of any hurricane or storm, because, while we shall go through the tail at great velocity, the density .will be so slight that such an effect will be utterly out of the question. Tlje gas is at a pressure of less than one-thousandth part of the pressure of the atmosphere. It is as tenuous as the most perfect vacuum one can make with an air pump. Now, you will agree that if I could throw a vacuum—not the vessel containing it, but' only the vacuum—at you, it would not hurt you, however hard I threw it. A blow from a comet's tail is like that. In fact the comet's tail is the nearest thing to nothing that we have any knowledge of. The atmosphere around the earth is like plate armour to ward it off." "Not Creditable to Wellington." What special observations will be taken in New Zealand and elsewhere? "\VTierever there is an adequate telescope, observers will doubtless try to photograph the transit of the head of the comet across the sun's disc. At Meeanee photographs of the sun will be taken every two or three minutes during the hour of transit, and I expect tho same will be done at Wanganui. Tho transit will be invisible to the naked eye, and there is only a more possibility of some impression being made on a photographic plate attached to a camera. There is more probability of an image of the comet being obtained by means of the spectre-heliograph, but only a few telescopes in the world are fitted with this apparatus, • and none in Australasia. I should like to say that I think it is not very creditable to Wellington that there is no telescope here by means of which any good observations of the transit could be made. It is a pity that no movement is being' mado to provide tho city with a good telescope." Shall wo be able to perceive any increase of temperature when we enter the tail? "No. The glow of the tail is not due to a high temperature, but to electrical discharges in gas at a low pressure. The tail is not very hot." The Rev. Dr. Kennedy will have more to say on the comet to-morrow night, when he lectures at the Town Hall.