Pleasant Ways in Science - Richard Anthony Proctor

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the subject has had the effect of enlisting fresh recruits in the work of observation, and many of these may before long be heard of as among those who have employed Dr. Draper’s method successfully.

      But I would specially call attention to the interest which attaches to Dr. Draper’s discovery and to the researches likely to follow from it, in connection with a branch of research which is becoming more and more closely connected year by year with solar investigations—I mean stellar spectroscopy. We have seen the stars divided into orders according to their constitution. We recognize evidence tending to show that these various orders depend in part upon age—not absolute but relative age. There are among the suns which people space some younger by far than our sun, others far older, and some in a late stage of stellar decrepitude. Whether as yet spectroscopists have perfectly succeeded in classifying these stellar orders in such sort that the connection between a star’s spectrum and the star’s age can be at once determined, may be doubtful. But certainly there are reasons for hoping that before long this will be done. Amongst the stars, and (strange to say) among celestial objects which are not stars, there are suns in every conceivable stage of development, from embryon masses not as yet justly to be regarded as suns, to masses which have ceased to fulfil the duties of suns. Among the more pressing duties of spectroscopic analysis at the present time is the proper classification of these various orders of stars. Whensoever that task shall have been accomplished, strong light, I venture to predict, will be thrown on our sun’s present condition, as well as on his past history, and on that future fate upon which depends the future of our earth.

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      During the last five or six years a section of the scientific world has been exercised with the question how far the condition of the sun’s surface with regard to spots affects our earth’s condition as to weather, and therefore as to those circumstances which are more or less dependent on weather. Unfortunately, the question thus raised has not presented itself alone, but in company with another not so strictly scientific, in fact, regarded by most men of science as closely related to personal considerations—the question, namely, whether certain indicated persons should or should not be commissioned to undertake the inquiry into the scientific problem. But the scientific question itself ought not to be less interesting to us because it has been associated, correctly or not, with the wants and wishes of those who advocate the endowment of science. I propose here to consider the subject in its scientific aspect only, and apart from any bias suggested by the appeals which have been addressed to the administrators of the public funds.

      It is hardly necessary to point out, in the first place, that all the phenomena of weather are directly referable to the sun as their governing cause. His rays poured upon our air cause the more important atmospheric currents directly. Indirectly they cause modifications of these currents, because where they fall on water or on moist surfaces they raise aqueous vapour into the air, which, when it returns to the liquid form as cloud, gives up to the surrounding air the heat which had originally vaporized the water. In these ways, directly or indirectly, various degrees of pressure and temperature are brought about in the atmospheric envelope of the earth, and, speaking generally, all air currents, from the gentlest zephyr to the fiercest tornado, are the movements by which the equilibrium of the air is restored. Like other movements tending to restore equilibrium, the atmospheric motions are oscillatory. Precisely as when a spring has been bent one way, it flies not back only, but beyond the mean position, till it is almost equally bent the other way, so the current of air which rushes in towards a place of unduly diminished pressure does more than restore the mean pressure, so that presently a return current carries off the excess of air thus carried in. We may say, indeed, that the mean pressure at any place scarcely ever exists, and when it exists for a time the resulting calm is of short duration. Just as the usual condition of the sea surface is one of disturbance, greater or less, so the usual condition of the air at every spot on the earth’s surface is one of motion not of quiescence. Every movement of the air, thus almost constantly perturbed, is due directly or indirectly to the sun.

      So also every drop of rain or snow, every particle of liquid or of frozen water in mist or in cloud, owes its birth to the sun. The questions addressed of old to Job, “Hath the rain a father? or who hath begotten the drops of dew? out of whose womb came the ice? and the hoary frost of heaven, who hath gendered it?” have been answered by modern science, and to every question the answer is, The Sun. He is parent of the snow and hail, as he is of the moist warm rains of summer, of the ice which crowns the everlasting hills, and of the mist which rises from the valleys beneath his morning rays.

      Since, then, the snow that clothes the earth in winter as with a garment, and the clouds that in due season drop fatness on the earth, are alike gendered by the sun; since every movement in our air, from the health-bringing breeze to the most destructive hurricane, owns him as its parent; we must at the outset admit, that if there is any body external to the earth whose varying aspect or condition can inform us beforehand of changes which the weather is to undergo, the sun is that body. That for countless ages the moon should have been regarded as the great weather-breeder, shows only how prone men are to recognize in apparent changes the true cause of real changes, and how slight the evidence is on which they will base laws of association which have no real foundation in fact. Every one can see when the moon is full, or horned, or gibbous, or half-full; when her horns are directed upwards, or downwards, or sideways. And as the weather is always changing, even as the moon is always changing, it must needs happen that from time to time changes of weather so closely follow changes of the moon as to suggest that the two orders of change stand to each other in the relation of cause and effect. Thus rough rules (such as those which Aratus has handed down to us) came to be formed, and as (to use Bacon’s expression) men mark when such rules hit, and never mark when they miss, a system of weather lore gradually comes into being, which, while in one sense based on facts, has not in reality a particle of true evidence in its favour—every single fact noted for each relation having been contradicted by several unnoted facts opposed to the relation. There could be no more instructive illustration of men’s habits in such matters than the system of lunar weather wisdom in vogue to this day among seamen, though long since utterly disproved by science. But let it be remarked in passing, that in leaving the moon, which has no direct influence, and scarcely any indirect influence, on the weather, for the sun, which is all-powerful, we have not got rid of the mental habits which led men so far astray in former times. We shall have to be specially careful lest it lead us astray yet once more, perhaps all the more readily because of the confidence with which we feel that, at the outset anyway, we are on the right road.

      I suppose there must have been a time when men were not altogether certain whether the varying apparent path of the sun, as he travels from east to west every day, has any special effect on the weather. It seems so natural to us to recognize in the sun’s greater mid-day elevation and longer continuance above the horizon in summer, the cause of the greater warmth which then commonly prevails, that we find it difficult to believe that men could ever have been in doubt on this subject. Yet it is probable that a long time passed after the position of the sun as ruler of the day had been noticed, before his power as ruler of the seasons was recognized. I cannot at this moment recall any passage in the Bible, for example, in which direct reference is made to the sun’s special influence in bringing about the seasons, or any passage in very ancient writings referring definitely to the fact that the weather changes with the changing position of the sun in the skies (as distinguished from the star-sphere), and with the changing length of the day. “While the earth remaineth,” we are told in Genesis, “seed-time and harvest, and cold and heat, and summer and winter, and day and night, shall not cease;” but there is no reference to the sun’s aspect as determining summer and winter. We find no mention of any of the celestial signs of the seasons anywhere in the Bible, I think, but such signs as are mentioned in the parable of the fig tree—“When his branch is yet tender, and putteth forth leaves, ye know that summer is nigh.” Whether this indicates or not that the terrestrial, rather than the celestial signs of the progress of the year were chiefly noted by men in those times, it is tolerably certain that in the beginning a long interval must have elapsed between the recognition of the seasons themselves,

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