An examination of such enlarged photographs, which permits us to embrace with the eye a large surface, filled with a mass of nature-true details, has led MM. Loewy and Puiseux' to some interesting suggestions concerning the origin of the so-called "rills" or groups of parallel rents in the Moon's crust.' And on the other side of the Atlantic, the direct observations lately made by Professor W. Pickering under the clear sky of Peru, as well as his studies of the American photographs, have produced such new data concerning the atmosphere of the Moon, and the possible existence of water on its surface, as are sure to give a quite fresh interest to lunar studies." The Moon is so small in comparison with the Earth (its weight is eighty-one times less), and consequently the force of gravity is so much smaller on its surface, that, even if it had an atmosphere of the same composition as ours, its contain a mass of details which may be seen directly even with smaller telescopes, but had been overlooked; while the appearance of the same detail on two or three negatives settles all possible doubts as to its reality. (L. Weineck and E. S. Holden, "Selenographical Studies" in "Publications of the Lick Observatory," 1894, vol. iii.; Loewy and Puiseux, in "Comptes Rendus," tome cxix., p. 254, and tome cxxi., pp. 6, 79; Folie, "Bulletin " of the Belgian Academy, 1895, vol. xxix. No. 1; and Dr. Klein in "Sirius," 1895, p. 112.) 1.66 p. 79. Comptes Rendus," 8 juillet 1895, tome cxxi., 2 To explain the origin of these rents, Loewy and Puiseux look for the time when the rocks were in an igneous half-liquid state and floating islands of consolidated scoria were formed on the surface of the molten rocks and drifted like the ice-floes in the Arctic Ocean. Remaining in that sphere of ideas, it may, however, be remarked that the same rents might have originated when the whole crust was already solidified. When Lake Baikal is covered with a thick sheet of ice, and the level of the water goes slightly down in the winter, the ice is intersected by long rents, one to ten yards wide, which usually appear in about the same places and in the same directions. They run in straight lines, have vertical sides, and when the water at their bottom is frozen, they become miniature models of lunar rents. 8 William H. Pickering, "Investigations in Astronomical Photography," in "Annals of the Astronomical Observatory of Harvard College," vol. xxxii., part 1 (Cambridge, Mass., 1895). also Dr. Klein's analysis of the same ("Sirius," 1895, Hefte 7, 8, und 9). See density in its lowest parts would be. from thirty to fifty times less than the density of our atmosphere at the sealevel. But it appears from Dr. Johnstone Stoney's' investigations, that even if the Moon was surrounded at some time of its existence with a gaseous envelope consisting of oxygen, nitrogen, and water vapor, it would not have retained much of it. The gases, as is known, consist of molecules, rushing in all directions at immense speeds; and the moment that the speed of a molecule which moves near the outward boundary of the atmosphere exceeds a certain limit (which would be about ten thousand six hundred feet in a second for the Moon), it can escape from the sphere of attraction of the planet. Molecule by molecule the gas must wander off into the inter-planetary space; and, the smaller the mass of the molecule of a given gas, the feebler the planet's attraction, and the higher the temperature at the boundary of its atmosphere, the sooner the escape of the gas must take place. This is why no free hydrogen could be retained in the Earth's atmosphere, and why the Moon could retain no air or water vapor.. However, neither these speculations, which are very likely to be true, nor Bessel's previous calculations, could convince practical astronomers of the absolute absence of any atmosphere round the Moon. A feeble twilight is seen on our satellite, the twilight is due, as is known, to the reflection of light within the gaseous envelope; besides, it had been remarked long since at Greenwich that the stars which are covered by the Moon during its movements in its orbit remain visible for a couple of seconds longer than they ought to be visible if their rays were not slightly broken as they pass near to the Moon's surface. Consequently, it was concluded that the Moon must have 4 "On the Physical Constitution of the Sun and Stars," in "Proceedings of the Royal Society" for 1868; and paper "On the Cause of Absence of Hydrogen from the Earth's Atmosphere, and of Air and Water from the Moon," read on the 20th of April, 1892, before the Royal Dublin Society. some atmosphere, perhaps only two hundred times thinner than our own. Of course, a gaseous envelope so thin as that would only be noticeable in the deeper valleys, and it would attain its greatest density within the circus-like cavities whose floor, as a rule, lies deeper than the surrounding country. Towards the tops of the mountains it would be imperceptible. But nevertheless, as was shown by Neison, it would play an important part in the economy of life on the Moon's surface. The observations made at Lick, at Paris, and at Arequipa, fully confirm this view. A twilight is decidedly visible at the cusps of the crescent moon, especially near the first and the last quarter. It prolongs the cusps as a faint glow over the dark shadowed part, for a distance of about seventy miles (60"), and this indicates the existence of an atmosphere having on the surface of the Moon the same density as our atmosphere has at a height of about forty miles. A similar result is obtained when the slight flattening of the disc of Jupiter, which takes place when the planet is just going to be covered by the Moon, or emerges from behind it, is measured on the Arequipa photographs. Such an atmosphere is next to nothing, is but there another observation, namely, of a dark band appearing between Jupiter and the Moon's limb when the former begins to be covered by the latter; and Professor Pickering finds no other explanation for it than in some very light haze, partly due to water vapor, which would rise a few miles above the Moon's surface where it is illuminated by the rays of the Sun. Such a supposition would have been met some time ago with great suspicion. But it must be said that the more the Moon's surface is studied in detail the more astronomers are inclined to think that, in some places at least, a haze, originated from water vapor, is the only possible means to explain certain curious occurrences. Thus, Dr. Sarling has lately reminded us that, in 1774, Eysenhard, a pupil of Lambert, saw the part of the shadow line which crossed one of the plains (the Mare Crisium) In a wave-like movement brought in which lasted for two hours and was seen by three different persons-only in this part of the lunar disc. Those undulations, which spread at a speed of twelve hundred feet per second over a distance of eighty miles, could only be due-as Dr. Sarling truly remarks-to vapors floating over the plain.1 several instances, the interiors of deep lunar circuses took a misty appearance at sunrise, and this misty appearance disappeared as the Sun rose higher above the same circus, while in other cases it persisted a considerable time after sunrise, even though all around was sharply marked and distinct. And so on. The temperature of the Moon's surface, when it is heated by the Sun's rays, being very near to the freezing point, as appears from Langley's last the evaporation of measurements, frozen water under the rays of the ris ing Sun is surely not at all improbable. It remains, of course, to be seen whether a haze of this sort is not due in some cases to water ejected by volcanoes or geysers; the more so as some volcanic activity, remodelling until now the forms of the craters, seems to exist. There is, indeed, among astronomers a a lunar crater, strong suspicion of nearly three miles in diameter, being of recent formation. It was first dis covered by Dr. Klein in 1876, in the plain named Mare Vaporum, after he himself and many others had previously so often examined that region without seeing the crater. Besides, the alternate appearance and disappearance of another crater (Linné), nearly four miles in diameter, can hardly be ex plained unless it is concealed from time to time by the vapors which it itself exhales. As to changes observed in the shapes of small lunar volcanoes, ther are too numerous to be due to mere errors of observation." If free water thus exists occasionally. 1 "Sirius," 1895, vi., p. 134. 2 Edw. Neison, "The Moon and the Condition and Configurations of its Surface," p. 33 (Lo don, 1876). 3 The Observatory, June, 1892; xlvi., p. 134. Nature, rol even now, on the Moon's surface, or has existed at a relatively recent period, it is natural to ask whether it has left no traces of its activity. Are there no river-valleys which would bear testimony to its existence? Till lately, the majority of astronomers answered this question in the negative, even though their earlier predecessors, armed with feebler telescopes, were most affirmative on this point. The maria, or seas, are known to be plains on which no traces of aqueous action have been detected, and the clefts, or large "rills," are almost certainly rents produced in a solid surface. However, beside these clefts, there are much finer formations which only lately have received due attention, and these finer rills have all the aspects of river-beds. They are not straight-lined, but wind exactly as rivers wind on our maps, they fork like rivers; they are wider at one end than at the other, and one end is nearly always higher than the other. Many such fine rills have been observed and mapped lately, and Professor W. Pickering gives a list of thirty-five presumable river-beds, large, medium-sized, and very fine.1 However, contrary to most terrestrial rivers, the lunar river-beds-those, at least, which were observed by W. Pickeringhave their wider end in their upper course, nearly always in a pear-shaped craterlet. This circumstance offers, however, nothing extraordinary, as we know many rivers in Central Asia and South America which originate in a lake and grow thinner and thinner as they enter the arid plains. To take one illustration out of several, one such river, sixty-five miles in length with all its windings, rises in a craterlet, perhaps two thousand feet wide, but soon its valley, narrows to one thousand feet, or less, and is lost in a plain. Occasionally such "rivers" occur in groups on the slopes of the mountains. Other river-beds, on the contrary. seem to have the normal character of our rivers. One of them begins in the mountains as an extremely fine line, gradually in1 "Annals of the Astronomical Observatory of Harvard College, vol. xxxii., part 1, p. 87. LIVING AGE. VOL. XI. 566 creases in width, and, after having received a tributary, becomes a broad but shallow valley. Another bifurcates into two very fine lines in its higher part. In short, it may now be taken as certain that there are river-beds, to all appearance of aqueous origin; but they are so narrow that we should not be able to discover water-courses if they existed at the bottom of these valleys. We must be content with saying that they have been scooped out by running water. So much having been won, the next step was naturally to ask if no traces of vegetation can be detected. On Mars, we see how every year a snow cover spreads over the circumpolar region, how later on in the season wide channels appear in it, and how the snow thaws gradually-presumably giving origin to water; even clouds have lately been seen; and we can notice, moreover, how the coloration of wide surfaces changes, probably because they are covered with vegetation, and how that coloration gradually takes a reddish yellow tint. Of course, if anything of the sort took place on our nearest neighbor, the Moon, it would have been noticed long since. But it would be most unwise to maintain that nothing similar to it happens, on a much smaller scale. On the contrary, Professor Pickering shows that there are some probabilities in favor of plants of some sort or another periodically growing on the Moon as well. The great lunar circuses or craters attain, as is known, colossal dimensions; the largest of them have one hundred and one hundred and thirty miles in diameter, and the floor of their inner parts is mostly flat. Now, Neison had already made the remark that grey, almost black, spots appear on the floor of certain craters at full moon, but disappear later on, and W. Pickering has carefully investigated several such spots during his unfortunately too short stay at Arequipa. Contrary to all ex 2 Dr. Sarling's letter to "Sirius," March 30, 1895; map of the region near Herschel, f, made by J. N. Krieger at the observatory of Triest, in same periodical, September 1895, p. 195. century selenographers, who wanted to see on the Moon "fortifications," "national roads," and "traces of industrial activity;" such objects, if they did exist, could not be seen with our best instruments. But traces of vegetation which develops at certain periods and fades next, traces of water which runs perhaps even now, as well as indications of volcanic changes of the surface, become more and more probable in proportion as we learn to know our satellite better. pectations, they grow darker just after | last These observations,' which Professor 1 In the above-mentioned volume of "Harvard Annals" they are published in full, and are illustrated by a number of excellent photographs. II. When we examine the animal world in a descending series, from the highest animals to the lowest, we see how their organs of nutrition are gradually simplified, how they become less definite and less specialized in their functions, until we find that functions which are performed in higher animals by special glands are accomplished at the lower stages of the series by mere cells scattered in the tissues, or even by the The whole protoplasm of the body. same gradual simplification is seen in the organs of the senses. They also become less and less definite as we descend the scale; it becomes more and more difficult to separate them from each other, and in the lower invertebrates mere cells, disseminated in the tissues, answer more or less to the irritations from without. At last, at the very bottom of the series, the senseirritations are received by the whole surface of the animalcule's body. An immense amount of investigation has been made, especially within the last thirty years, in order to trace the chain of evolution of the sense-organs in the animal world, and to follow the gradual ascent of sense-impressions, from the mere irritability of protoplasm to the highly developed sensations of the higher animals. Anatomists, physiologists, and psycho-physiologists have joined in that colossal work, and by this time it may be said that a result of the highest importance for science altogether, and especially for psychology, has been attained. The series has gradually been reconstituted in full, through the efforts of scores of separate workers. | lately observed under the microscope The leading results of these wonderful investigations having lately been summed up by Dr Wilibald Nagel in a suggestive introductory chapter to a more special work;1 we may take it, together with a few other works, as a guide for a brief review of the subject.' What most strikes a beginner in the study of the lowest animals is the variety of those of their acts and motions which apparently imply psychical life and consciousness. Those microscopical animalcules which consist of one single cell, or even of a mere speck of protoplasm, have evidently no traces of a nervous system; and yet their movements and their responsivity to external stimuli are such that one hesitates to interpret them as mere mechanical or chemical processes, such as we see in foams, or even as mere manifestations of "irritability," which is a property of all living matter. In one of the American psychological laboratories, the daily life of a onecelled infusorium-a vorticella-was 1 Dr. Wilibald Nagel, "Vergleichend-physiologische und anatomische Untersuchungen über den Geruchs- und Geschmackssinn und ihre Organe; mit einleitenden Betrachtungen aus der allgemeinen vergleichenden Sinnesphysiologie," in Leuckart and Chun's "Bibliotheca Zoologica," Heft 18, I. and II. (Stuttgart, 1894 and 1895). A full bibliography will be found at the end of this work. for days in succession, and all the accidents of its uneventful existence were recorded. A transparent, tulip-like, or bell-like expansion at the end of a thin transparent stalk, which contracts at the slightest jerk; a tiny opening at the top of the bell, representing a sort of mouth, or rather a buccal pore; and a row of extremely fine cilia, which differ from hairs by being mere expansions of the protoplasm of the body—the whole, cilia and all, being covered with an extremely fine cuticle-such as that tiny infusorium which every one possessed of a small microscope can find in a drop of water taken from a pond. Observed hour after hour under the microscope, while a feeble current of water was flowing over the glass slide, it was seen to swallow still smaller animalcules, after having attracted them into its "mouth" by the motion of its cilia; it assimilated them, and being well provided with food, it reproduced itself by budding tiny vorticellæ from its sides. To many stimuli it was insensible. Icy water was made to flow; bright light, immediately following darkness, was flashed upon the little creature; light of various colors was tried, as also musical sounds "of all qualities and volumes"-the animalcule took no heed of them. But the slightest jerk or jar made it instantly contract its stalk; and it sorted with the greatest apparent precision the floating minute particles. swallowing those of them which suited it. "The world of relation," as psychol 2 E. Jourdan's "Les Sens chez les Animaux Inférieurs (Paris, J. Baillière, 1889) is an excellent little work on the same subject which can be safely recommended to the general reader. Unhappily it has not been translated into English. Haeckel's "Essay on the Origin and Development of Sense-ogists say, of a vorticella thus consists Organs" (English translation) dates from 1879. Romanes's "Mental Evolution in Animals," Sir John Lubbock's "The Senses and the Mental Life of Animals, especially of Insects," and C. Lloyd Morgan's "Introduction to Comparative Psychology," published in 1894, although they do not exactly cover the same ground, are too well known to need recommendation. W. Wundt's "Grundzilge der physiologischen Psychologie" (4th edition, Jena, 1894), and Max Verworn's "Allgemeine Physiologie" are, of course, two classical works, rich in information upon the subject as well, but neither has yet been translated into English. Wundt's "Lectures on Human and Animal Psychology have at last been translated into English in 1894. Some works on the lower organisms are indicated further on. of a series of touches, with perhaps some taste and smell impressions, hardly distinguished from each other, With all that, the vorticella displayed memory. When no other food was supplied to it but cells of yeast in sterilized water, it took first to the new food. It filled its body to distension with yeast cells; but in a few minutes the entire meal was suddenly rejected, and for several hours the vorticella could not 3 C. F. Hodge and H. A. Atkins, "The Daily Life of a Protozoan," in American Journal of Psychol ogy, 1894-95, vol. vi., p. 524. |