Part 11

The last few years of the century were rendered memorable from the lunar point of view by the publication and minute study of a most admirable series of photographs of the moon obtained by the great equatorial Coudé of the Paris Observatory by Loewy and Puiseaux. One of the chief points aimed at has been to determine the sequence of the various events represented by the rills, craters, and walled plains, the mountain ranges and seas. This work is still in progress, the fourth part of the atlas being published in 1900; but enough has already appeared to indicate that the results of the inquiry when completed will be of the most important kind. The authors have already come to the conclusion that the lunar and terrestrial sea-bottoms much resemble each other, inasmuch as both have convex surfaces. The lunar seas began by sinking of vast regions; the formidable volcanic eruptions of which the moon has been the scene have taken place in times equivalent to those labelled “recent” in geological parlance. There is evidence that the axis of the moon has undergone great displacements, and four great periods of change have been made out. Finally they state that there is serious ground to believe that there is an atmosphere of some sort remaining.

It may readily be understood that with each increase of optical power new satellites of the various planets have been discovered. Soon after the discovery of Neptune a satellite was noted by Lassell. In 1846 both he and the eagle-eyed observer Dawes independently discovered another satellite (Hyperion) of Saturn. Lassell was rewarded in the next year by the discovery of two more satellites of Uranus; but, strangest observation of all, in 1877 Hall discovered at Washington two satellites of Mars some six or seven miles only in diameter, one of them revolving round the planet in seven and one-half hours at a distance of less than four thousand miles. As the day on Mars is not far different in duration from our own, this tiny satellite must rise in the west and south three times a day!

Wonderful as this discovery was, it is certainly not less wonderful when we consider it in connection with a passage in _Gulliver’s Travels_, so true is it that truth is stranger than fiction. Swift, in his satirical reference to the inhabitants of Laputa, writes: “They have likewise discovered two lesser stars, or satellites, which revolve round Mars, whereof the innermost is distant from the centre of the primary planet exactly three of his diameters and the outermost five; the former revolves in the space of ten hours; and the latter in twenty-one and a half.”

The last discovery of this kind has been that of an inner satellite of Jupiter by Barnard in 1892.

The planets from Mercury to Saturn were known to the ancients. I have already referred to the discovery of Uranus by Herschel’s giant telescope, not long before the nineteenth century was born, and of Neptune, by analysis, towards the end of the first half of the century. With regard to what modern observations have done in regard to their physical appearance, the first place in general interest must be given to Saturn and Mars.

Saturn has always been regarded as the most interesting of the planetary family on account of its unique rings. Many subdivisions of the rings, and a dusky ring, first seen by Dawes and Bond, have been discovered during the last sixty years.

The meteoritic nature of the rings was suggested by Clerk Maxwell in 1857, and Keeler’s demonstration of the truth of this view by means of the spectroscope, a few years ago, was brilliant in conception and execution.

But during the last half of the century the interest centred in Mars has been gradually increasing. The drawings made during the opposition of 1862, when compared with those made by Beer and Mädler (1830–40), made it perfectly clear that in this planet we had to deal with one strangely like our own in many respects. There were obviously land and water surfaces; the snow at the poles melted in the summer-time; clouds were seen forming from time to time, and the changing tones of the water surfaces suggested fine and rough weather.

Afterwards came the revelation of the hawk-eyed Schiaparelli, beginning in the year 1877, and his wonderful map of the planet’s surface. The land surfaces, instead of being unbroken, were cut up, as an English farm is cut up by hedges; straight lines of different breadths and tints crossed the land surfaces in all directions, and at times some of them appeared double. Schiaparelli naturally concluded that they were rivers—water channels—and being an Italian he used the appropriate word _canali_. This, unfortunately, as it turned out, was translated _canals_. Now canals are dug, _ergo_ there were diggers. From this the demonstration, not of the habitability, but of the actual habitation, of Mars was a small step, and the best way of signalling to newly found kinsmen across some thirty millions of miles of space was discussed.

The world of science owes a debt of gratitude to Mr. Percival Lowell for having taken out to the pure air and low latitude of Arizona an eighteen-inch telescope for the sole purpose of accumulating facts tending to throw light upon this newly raised question. This he did in 1894. Schiaparelli has continued his magnificent observations through each opposition when the planet is most favorably situated for observation, and since 1896 Signor Cerulli, armed with a fifteen-inch Cooke, in the fine climate of Italy, has joined in the inquiry, so that facts are now being rapidly accumulated. It has been stated that markings similar to the strange so-called “canals” on Mars are to be seen on Mercury, Venus, and even on the satellites of Jupiter. Mr. Percival Lowell does not hesitate to proclaim himself in favor of their being due, _in Mars_, to an intelligent system of irrigation. Signor Cerulli claims that _wherever seen_ they are mere optical effects. We may be well content to leave to the twentieth century a general agreement on this interesting subject.

Finally, in our survey of our own system, come comets and meteor swarms. One of the most fruitful discoveries of the century, that comets are meteor swarms, we owe to the genius of Schiaparelli, A. H. Newton, and other workers on those tiny celestial messengers which give rise to the phenomena of “falling” or “shooting” stars.

The magnificent displays of 1799, 1833, 1866, and, alas! that which failed to come in 1899, we now know must be associated with Tempel’s Comet. This is by no means the only case so far established; the connection will in the future be closer still when the orbits of the various swarms observed throughout the year shall be better known.

Comets which attract public attention by their brightness and grandeur of form are rather rare, and, in fact, only twenty-five of such have been seen since 1800. We have, however, with the great advance in instrumental equipment, been able to discover many which are scarcely visible to the naked eye, and this has swollen the number of comets very considerably. In the seventeenth century we find that only thirty-two were observed, while in the eighteenth this number was more than doubled (seventy-two). In the nineteenth century more than three hundred were placed on record, which is practically more than four times the number seen in the eighteenth.

The last great comet visible any considerable time was that discovered by Donati in 1858, and so carefully observed by Bond. It is unfortunate that since the importance, in so many directions, of spectroscopic observations of comets has been recognized they have been conspicuous by their absence.

THE CONNECTION BETWEEN SOLAR AND TERRESTRIAL WEATHER

Everybody agrees that all the energy utilized on this planet of ours, with the single exception of that supplied by the tides, comes from the sun. We are all familiar with the changes due to the earth’s daily rotation bringing us now on the side of our planet illuminated by the sun, then plunging us into darkness; that changes of season must necessarily follow from the earth’s yearly journey round the sun is universally recognized.

On the other hand, it is a modern idea that those solar phenomena which prove to us considerable changes of temperature in the sun itself, may, and indeed should, be echoed by changes on our planet, giving us thereby an eleven-year period to be considered, as well as a year and a day.

This response of the earth to solar changes was first observed in the continuous records of those instruments which register for us the earth’s magnetism at any one place. The magnetic effects were strongest when there were more spots, taking them as indicators of solar changes. Lamont first (without knowing it) made this out, at the beginning of the latter half of the century (1851), from the Göttingen observations of the daily range of the declination needle. Sabine the next year not only announced the same cycle in the violence of the “magnetic storms” observed at Toronto, but at once attributed them to solar influence, the two cycles running concurrently. It is now universally recognized that terrestrial magnetic effects, including auroræ, minutely echo the solar changes.

The eleven-year period is not one to be neglected.

Next comes the inquiry in relation to meteorology. Sir William Herschel, in the first year of the century, when there were practically neither sun-spot nor rainfall observations available, did not hesitate to attack the question whether the price of wheat was affected by the many-or-few-spot solar condition. He found the price to be high when the sun was spotless, and _vice versa_.

By 1872, however, we had both rainfall and sun-spot observations, and the cycle of the latter had been made out. Meldrum, the most distinguished meteorologist living at the time, and others, pronounced that the rainfall was greatest at sun-spot maximum, and, further, that the greatest number of cyclones occurred in the East and West Indies at such times.

This result with regard to rainfall was not generally accepted, but Chambers showed shortly afterwards an undoubted connection between the cycles of solar spots and barometric pressure in the Indian area.

By means of a study of the widened lines observed in sun spots an attempt has been recently made to study the temperature, history of the sun since about 1877, and the years of mean temperature and when the heat was in excess (+) and defect (-) made out, have been as follows:

Heat condition mean + mean − mean + mean − mean Years 1869 1876 1881 1886–87 1891–92 1870–75 1877–80 1882–86 1881–91 1892

Having these solar data, the next thing to do was to study the Indian rainfall during the southwest monsoon for the years 1877–1886, the object being to endeavor to ascertain if the + and − temperature pulses in the sun were echoed by + and − pulses of rainfall. The Indian rainfall was taken first because in the tropics the phenomena are known to be the simplest. It was found that in many parts of India the + and − conditions of solar temperature were accompanied by + and − pulses, producing pressure changes and heavy rains in the Indian Ocean and the surrounding land. These occurred generally in the first year following the mean condition, that is, in 1877–78 and 1882–83.

The rainfalls at Mauritius, Cape Town, and Batavia were next collated to see if the pulses felt in India were traceable in other regions surrounding the Indian Ocean to the south and east. This was found to be the case.

A wider inquiry was followed, we are told, with equal success, so that we are justified in hoping that the question of the dependence of terrestrial upon solar weather has made a step in advance.

But just as the general public and practical men took little heed of the connection between sun spots and magnetism until experience taught them that telegraphic messages often could not “get through” when there were many sun spots, so the same public will not consider the connection in regard to meteorology unless the forecasting of droughts and famines be possible.

The recent work suggests that, if the recent advances in solar physics be considered, the inquiries regarding rainfall may be placed on a firmer basis than they could possibly have had in 1872, and that such forecastings may become possible.

What was looked for in 1872 was a change in the quantity of rain at maximum sun spots only, the idea being that there might be an effective change of solar temperature, either in excess or defect, at such times and that there would be a gradual and continuous variation from maximum to maximum.

We see that the rainfalls referred to above justify the conclusions derived from the recent work that two effects ought to be expected in a sun-spot cycle instead of one. There was excess of rainfall, not only near the sun-spot maximum, but near the minimum.

If the authors of this communication to which I refer are right, then droughts and famines occur in India because the rain pulses, which are associated with the solar-heat pulses, are of short duration. When they cease the quantity of rain which falls in the Indian area is not sufficient, without water storage, for the purposes of agriculture; they are followed, therefore, by droughts, and at times subsequently by famines. They divide the period 1877—89 as under:

{ 1877. Rain from − pulse { 1878. { 1879 (part).

{ 1879 (part). No rain pulse { 1880 (central year). { 1881 (part).

{ 1881 (part). { 1882. Rain from + pulse { 1883. { 1884 (part).

{ 1884 (part). { 1885 } No rain pulse { 1886 } (central year). { 1887 (part).

{ 1887 (part). Rain from − pulse { 1888. { 1889.

Their statement is based on the fact that all the famines which have devastated India for the last seventy years have occurred at intervals of eleven years, or thereabouts, working backward and forward from the central years 1880 and 1885–86 in the above table, the middle years, that is, between the pulses.

Mr. Willcocks, in a paper read at the Meteorological Congress at Chicago, remarked that “famines in India are generally years of low flood in Egypt.”

It is now pointed out that the highest Niles follow the years of the + and − pulses, as does the highest rainfall in the Indian area.

Even if these results, which were communicated to the Royal Society of London five weeks before the end of the century, be confirmed, it may be pointed out that Sir William Herschel’s suggestion of 1801 will have required a whole century for its fulfilment, so slowly do those branches of science move which have not already led to some practical development.

NORMAN LOCKYER.

PHILOSOPHY

It is a natural illusion that makes us think of each century as exhibiting the continuous development of one tendency of mind through a series of stages whose differences are only of secondary importance, and, on the other hand, to regard the steps from one century to another as corresponding to some marked transition of thought, as if the world had been suddenly precipitated into a new sphere of existence. For some purposes a rough generalization of this kind, that breaks at stated intervals the continuity of time, may, perhaps, be convenient. When, however, we begin to look at things more closely, we discover that it is impossible thus to cut through the historical connection of events, as it were, “with a hatchet.” We discover, for example, that the characteristics of the eighteenth century were strongly marked only in one period of it; and that what we call the spirit of the nineteenth century was born some time before the year 1800, and has never quite prevailed over other tendencies. At the same time, there is an important difference indicated by these two loosely used names, and as it is always easier to define things by contrast, it may help us to make our subject more definite to consider what they mean.

I

It is too late now to “abuse the eighteenth century,” which had its good and evil, like other periods. It is commonly conceived as the era of individualism and analysis, the era of logical enlightenment and sceptical criticism; and, again, as the era of liberation from groundless superstitions and fictitious claims of authority; the era in which mankind seemed for the first time to throw off the weight of the past and to enter without fear upon the enjoyment of their earthly heritage. The science of Newton had given the last blow to the astronomy that made the earth the centre of the universe. It had undermined and discredited the simple theology that explained the whole material world as a cosmos arranged for the supply of human needs. At the same time, the progress of biology was bringing man to a consciousness that as a physical being he is only _primus inter pares_ in the animal kingdom, and the decay of religious belief was making him realize his finitude, the limits of his natural existence, as, perhaps, he had never done before, at least never since the beginning of the Christian era. Earth seemed to be disconnected from heaven, and the human race thrown upon its own resources. By the new enlightenment all powers, ecclesiastical or political, were stripped of the mysterious sanctity that had once invested them. “The nimbus was taken away from the heads of the gods and rulers of the world.” Every authority that claimed man’s homage was weighed in the scales of the understanding, and, so weighed, every such authority was found wanting. The State had come to be regarded as only a collection of individuals who had agreed to live together under a ruler deriving all his claims from their consent, and invested with no divine right to their allegiance. The Church was no longer a sacred institution governed by priests who held their commission directly from God, but only a sort of spiritual police agency, an ally of the State in the restraint of vice and crime, or, at best, in Protestant countries, a society for mutual improvement. Men were “free and equal,” each standing face to face with his fellows, admitting no superiority or superstition of hero-worship in regard to any one of them. And the Deity, if his existence were not denied, tended to become a mere “Supreme Being,” who was removed to such a distance from mankind that he could hardly be reached by their reverence, still less by their love.