Sun Searchers Romance of the Sun. By Mary Proctor, F.B.A.S.,
F.B.Met.S. •• (Harper. 7s. 6d.) Xni the year 1610 a telescope was used for the first time in Man's observation of the sun, moon, and stars: The universe was literally thrown open to him. Not for another 250 years, howeVer, was much progress made in the study of the sun. for this vast changing mass, shielded by its own brilliance, refused to yield the secret of its structure to the prying lenSes of the telescope. A few discoveries were made, which had been hidden even from the naked eye of the patient Greek philosopher star-gazers. The telescope showed, for instance, a hitherto unseen darkening of the solar surface towards the circumference. Galileo also Totted certain dark'spots which he supposed to be clouds floating in the solar atmosphere. The idea of such possibility of blemish was scorned by his con- temporaries, for in those days the doctrines of the Greeks, and particularly of Aristotle, were still sacred, and conse- quently the immaculate nature Of the sun was *accepted as a fundamental law. • - --.
Galileo, however, doggedly persisted in his experimental observation through the rough-and-ready telescopes made by his own hands. In his eagerness he often neglected to use the clouded lenses such as are now used, and in consequence he loSt his sight.
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Galileo's truly scientific beginnings in the Study of the sun led the way to a substantial body of knowledge-relating to the sun's habits. But apart from that, very little' progress was Made. Only 130 years ago the greatest genius of astro- nomical thought, Sii William Herschel, advanced the theory that the sun was " a large and lucid planet, the only primyry one of our system." He went on to expound the supposition that it consisted of a solid and even inhabitable body, sur- rounded " by protective clouds, dense; opaque, and highly reflective, which must add a most capital support to the splendour of the Sun by throwing back so great a share of the brightness coming to them." Observing the changing surface Of the sun, he decided that this was due to the movement of a cloud envelope, and indicated the action of storms and hurricanes, This cloud layer was periodically torn open, to ethit what he called " empyreal. gas," which, ascending,
Spread outward and mingled with other superior gases."
In -spite of all this violence, Herschel considered that it /eight he admitted that the sun " Was' richly stored with
inhabitants." He argued that all the glory and blaze were merely superficial, and that beneath the luminous curtain of the planetary clouds was a calm and stable world capable of producing and supporting conscious life. Even as late as 1846 we find this delightful fantasy referred to as the prevailing theory.
The death-blow was given to all these fantasies by the invention of the spectroscope. As early as 1675 Newton had experimented -in a darkened room with a glass prism which he had placed directlY in the path Of a beam of sunlight shining through a round hole in a shutter. On the opposite wall was thrown a rainbow-coloured image of the sun. This is A.B.C. to us all now ; but it was the beginning of a vast and beautiful branch of the divine science which still is being
developed. • -
In 1802 the astronomer Wollaston first noted that when light is admitted to a prism--or spectroscope—through a narrow slit, numberless lines appear amongst the -primary colours. In 1814 a Munich optician named Fraunhofer located 576 of these lines, but another half-century passed before their significance Was- discovered. It was then found that specific lines appeared at the refraction of the rays from specific incandescent elements. Thus the vapours of sodium, calcium, iron were found to have each its own lines in the gamut of the spectrum. It will be seen that immediately this .diScoerY was made a key to the actual chemical analysis of the sources of rays reaching us from heavenly bodies was put into the astro- nomers' hands. In particular, knowledge of the composition of the sun -became possible, and it was not until then that astro-physies. becairie -as it were le fully enabodied science, amplifying and giving life-breath to the skeleton 'pieced together by the mathematicians.
The principal function of Miss Proctor's book is to show how the spectroscope has been developed, so that we now have marvellous instruments by which- the sun, in -all its fiery eccentricities, may be photographed, and so measured and named in its constituent elements. The amateur should find the book very useful. The author has also brought together a number of graphic accounts of total eclipses, the best of which are those by • observers in aeroplanes of the
-BICHAR6 €HILTHCH.
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