THE SECRETS OF HALLEY'S COMET.

Wairarapa Age, Volume XXXII, Issue 9991, 10 March 1910, Page 7

THE SECRETS OF HALLEY'S COMET.

PROBLEM OP 1 lIS POISONOUS TAIL.

Will the tail of llalley's famous comet sweep the earth in its course, and, if so, will the gases in its tail be deadiy and poisonous? Ir some photographs just taken by the astronomers, Messrs Frost and Parkhurst, the light of Halley's comet has been shown to be largely due to the poisonous cyanogen. How can we find out these things? How does the astronomer know what is burning in the atmosphere of a star thousands of millions of miles away? As a matter of fact, he not only can tell largely what these distant suns contain but the exact speed at which a star is approaching or receding from our earth. The extraordinary revelations of recent years are due very largely to the instrument known as the spectroscope, which can be most readily understood by a simile. buppose a chord is played on the piano, and while the fingers are still on the notes their position is ascertained. We could then find out the notes which made up the ! chord Then suppose that some big ' noise were made, and when yu found out that were responsibla, for it you discovered that every rote in the piano had been struck simultaneously. Now let us regard ths sunlight, that is to say, ordinary white light, as the big noise, and pass a beam of this light through a prism. The prism splits up the white light into coloured rays, violet, blue, green, yellow, orange and red. of every imaginable shade, and light of each shade lies close beside the next just like the key's of the pinao. The light from a certain star is like the chord that was struck; examined by means of the prism we should see it 3 "notes"-—we should perhaps see a blue "note," a green note, and two or three orange and red notes.

In this case the rotes would be called lir.es, and just as a note struck on the piano sounds because waves of the air are caused which give the impression of sound to our ears, so a bright coloured line in the spectrum (the analogue of the keyboard) is due to waves of a definite number per second in the ether that - is said to f>6rva<?e all space. Certain chemical substatieg giv6 ceftsin coloured lines in the spectrum. If you used an instrument provided with a prism called a spectroscope, and looked at a flame in which ordinary kitchen salt was being burnt you would see two bright yellow lines which any chemist or astronomer could tell j you was caused by the metal sod- I ium, of which salt is in part composed. If, then, the astronomer arranges a telescope with a spectroscope he sees the light from a star split up in • to coloured lines and bands, or usually he sees dark lines denotirg the various colours by their position relative to the various colours in the spectrum. THE POISONOUS CYANOGEN GAS. j Now, suppose that an astronomer is examining Halley's comet through the spectroscope. He may see perhaps a dark band or bands; he measures carefully their position and wave length; if they correspond to those of a certain known substance, then the poionous gas cyanogen will be present. Such bands recently indicated to Professor Lowell that the atmosphere ! of Mara contained oxygen—the ele- ( ment essential to human life; others J have indicated water vapour, while i quite recently bands suggesting the actual colouring matter of foliage and flower have been discovered in speatro photographs of some of the planets! The immense telescope at the YerkesObservatory at Chicago has an i objetive lens 40in in diameter, and to the eye-piece of this magmfient refractor is fitted a Bruce spectrograph which photographs the lines and bands in the stars' spectra. J Once the star is in the field of the I telescope the latter is actuated by ! clockwork and the star kept in view. The light of the star, instead of being viewed by the eye, is focu c sed on a fine slit about a hundredth of an iich wide, and it goes- thence through a lens to the prism; the star image is kept on a slit until enough exposure | h?a been given to record the line? or ! bands on fa photographic plate, and i thus a permanent record is obtained. I Hundreds of astronomers in varj ions parts of the world are preparing now to obtain such records of ! the famous Halley comet, and very * soon we shall know quite a lot about 1 the composition of its nucleus, its tail, and, in fact, everything in connection with it.