But you may say, How do you know that we must of course presume that they are unthose other worlds are not composed of such inhabited.

materials that life is there impossible? Sci- The first planet outside of the Earth-Mars ence has within the last few years stretched-is 50 millions of miles more distant from the her hand across the almost immeasurable dis- Sun than we are. When it is favorably situtances which separate us from the fixed stars, ated its surface can be closely scanned through and told us that there are in them many of the the telescope. It seems to me to be by far substances with which we are here familiar. the most interesting object in the heavens from It would lead us too far from our subject to its similarity to the Earth. indicate the manner in which so grand a result has been reached. I can only tell you that we are able, by examining the light coming from the stars by a prism, to detect their composition, just as if we had fragments of them in our laboratories. Spectrum analysis has made the chemist's arms millions of millions of miles long.

Let us examine our planetary neighbors, and ascertain what are the chances of inhabitation upon them. The two planets that are nearer to the Sun than the Earth may be dismissed at once. The most reliable researches lead astronomers to suppose that Mercury and Venus are too hot to permit of either animal or vegetable life. Venus ís regarded as being red-hot, and Mercury even hotter. If such be the case,

In the summer of 1862, when my large telescope had been completed, Mars was often observed, and showed appearances some of which are represented in the adjoining cut drawn by Professor Phillips. There was visible, in the first place, an expanse of water covering a large proportion of the Southern hemisphere, and of a greenish hue. The remaining parts, at the upper portion of the picture, are land of a reddish tinge, assuming the figure of continents. In addition-and this is a point of peculiar interest-at the north and south polar regions there are accumulations of snow, presenting appearances strictly analagous to those at the arctic and antarctic regions of our globe. The snow spot at the South Pole is here shown; the North Pole is invisible.

his year is almost equal to two of ours, each season is twice as long as with us.

Let us recall the condition of our Northern | a warm summer and a cold snowy winter. As Hemisphere. In winter snow falls and covers it with a white envelope, extending for six months, to a latitude certainly as low as the northern border of the United States. If the carth were viewed from a distance, there would seem to be a white spot surrounding the north pole. As summer came on this white spot would begin to disappear, melting away at its southern border, and to the distant observer would seem quite insignificant at midsummer. Precisely a similar phenomenon is witnessed at the poles of Mars, and hence we see that he too has seasons similar in their nature to ours, VOL. XXXIII.-No. 193.-D

There is still another point of resemblance. On watching the planet Mars carefully through a large telescope, we observe that his surface is not always the same in appearance, but that dark spots occasionally are visible, and cover large parts of it. They are variable in extent and outline. These are obviously clouds floating in his atmosphere, the source whence falls the winter's snow and, doubtless, though we do not see it, the summer's rain.

There is then another body, revolving as the

Earth does around the Sun, as far as we can judge suited to the abode of sentient beings. It has air, water, alternations of seasons, snow, rain, and, possibly, vegetation. It is, to be sure, half as far again as we are from the Sun, the source of light and heat, but is not cold enough to be perpetually frozen and therefore sterile.

the dark spots were called seas, the bright ones land. But we now know that there is not any large collection of water on the side of the Moon that is turned toward us. Why is that expression, "the side turned toward us," used? We only see one hemisphere of the Moon; one side is perpetually turned away from us.

A telescope of even moderate power shows at once, particularly if the Moon be only six or eight "days old," that her surface is very rugged and much broken. The northern part is less rugged than the southern, and we see that the so-called seas are great valleys many hundred miles across. They may be the basins in which seas formerly were, but they now contain no water. Nor do we find on any part of the visible side tokens of either air or water. Recall

The question at once arises, do you discover upon its surface any traces of the works of man, are there tokens of great cities and visible lines of road? As our telescopes are at present, we are too far off to see any of these things, even if they are there. No power yet applied would enable us to distinguish at this distance an object 50 miles square. What we may do in the future it is, of course, impossible to predict. One of the greatest obstacles to distinct visioning the fact that no animal or plant can live is our own atmosphere. Its currents and motions tend to confuse the outlines of objects, and, according to my experience, a whole year may pass without the occurrence of more than one good night. The only remedy is to carry the telescope as high up on a mountain as possible, so as to leave below the more injurious portions of the atmosphere. It might be possible to work 15,000 feet above the sea in the neighborhood of the equator.

But you will say why is the Moon overlooked all this time? She is close to the Earth, and must possess similar conditions as to light and heat; are not the probabilities strong that she is inhabited?

without these essential materials, we are convinced at once that there is no use in searching for inhabitants there.

But there are strong reasons for believing that water must exist somewhere on the Moon. That fluid enters as an ingredient into the composition of rocks, and it is a cause of volcanic eruptions. The face of the Moon is largely composed of abrupt rocky precipices, and volcanic action has been in past ages frequent on it.

In the list of planets given, four large ones were placed outside of Mars, that is, farther from We are sure that the water is not floating the Sun. But with these we have not time to about in the shape of dense clouds, for we deal. The only remark necessary to be made should see them easily enough through our telis, that on two of them, Jupiter and Saturn,escopes, and collections of ice and snow would there is reason to believe both air and water now and then make their appearance. Of late, exist. however, it has been demonstrated mathematically, that the side nearest to us is farther away from the Moon's centre of gravity than the more distant side. It is, so to speak, down hill from this face to that, the amount of declivity being about 30 miles. So there might be air and water 30 miles deep on the opposite side, and we should not see them here. There may be inhabitants there, but our chances of making their acquaintance are small enough. It was at one time proposed by some enthusiastic astronomers to communicate with the inhabitants of the Moon by erecting on one of the great plains of Asia stone structures representing a certain geometrical problem, "in a right-angled triangle the square of the hypothenuse is equal to the sum of the squares of the other two sides." It was hoped that if there were intel

A few years ago there was published in the daily papers of this city a description of pretended discoveries in the Moon which excited at the time a great deal of attention. It was stated that Sir John Herschel had taken to the Cape of Good Hope a lens of 24 feet diameter, and with it had seen a variety of objects, animals, buildings, and even a species of men. The human beings were described as having wings like a bat, but nevertheless they evidently conversed and were familiar with polite actions, such as peeling fruit for one another. This, "the Moon Hoax" as it is termed, im-ligent inhabitants on the Moon who had disposed on very many persons, and when its falsity was discovered, left behind an unfortunate skepticism as to statements that are really

true.

Let us examine the actual state of the Moon, and see what the probabilities of habitation are. We will ascertain the more prominent peculiarities, and then I will show you some of them by the aid of a photograph enlarged by Starr's calcium light and lens.

On looking at the Moon with the naked eye certain markings are visible, dark and white spots. Before the invention of the telescope

covered the truths of geometry they would answer by marking out on one of their plains some other problem in response.

We see from our physiological investigation of the subject how futile such an attempt would have been. The inhabitants on the far side of the Moon, if there are any such, never see the Earth unless it may be low down in the horizon and dimly. If they existed on the centre of this side, they would see her as a glorious globe, fourteen times as large as the Moon seems to us, shining with a pure light, variegated with clouds, and revolving like a gigantic

clock directly overhead. Now Europe, Asia, and Africa would be visible; in a few hours they would set, and North and South America, in their turn, come into view. They would have no need of watches. Our large cities would be visible through a telescope, a spot 500 feet square being distinctly perceptible. But it is of no use to speculate on the appearance of things that are not seen.

this city. The reason that so large an instrument is demanded-for this is the largest reflector in use in America-is, that a great amount of light must be collected to get a photograph of such a size that it will bear magnifying, and yet can be taken quickly. The problem is just the same as in portrait photography-the larger the lens the more quickly can a picture of a given size be taken. It was ignorance of this fact that led Daguerre, who invented the daguerreotype process, to declare that human portraits could not be taken photo

So far from perceiving any visible traces of human habitation on the Moon through our telescopes, she presents to the eye only a desolate sterile waste. There are no tokens of activ-graphically. According to his ideas, and with ity. Even her volcanoes are extinct. We are able to determine now with precision their unchanged condition by the aid of photographs taken from time to time. They show no change though an interval of years may have elapsed. It is true, nevertheless, that minute changes may be occurring, for the difficulties of obtaining first-class photographs are so great that slight eruptions might be overlooked.*

his apparatus, it was necessary to sit more than two hours, and that requires more patience or stolidity than most of us have. My father, however, overturned this idea, and in 1839 succeeded in the University of this city in getting the first portrait from life. One of the earliest is still in existence in the possession of Sir John Herschel, who states that it is as good as when first made.

The taking of a photograph of the Moon may In the enlarged photographic view which you be compared to getting the likeness of a man are going to see upon the screen there are many who is rapidly walking. We can not fasten her points to which your attention might be directed. with a clamp as they do one's head at a photog-Of these we shall select only a few, as a full exrapher's establishment, it is necessary to neu-planation of all would demand too much time.* tralize the motion by another precisely similar. You will perceive, in the first place, that the This fortunately we can accomplish by fine whole circular face of the Moon is not presentclock-work so contrived as to make the telescope ed to you; only one semicircle is visible. The by which the photograph is taken point stead- photograph is taken from the Moon in her third ily at the same part. But there is another mo- quarter, when she was 21 days old, because at tion we can not neutralize, arising from the that time it better exhibits the more striking tremors of our air. Any one who has looked peculiarities than when full. You will remark across the top of a hot stove at objects beyond that the semicircle is diversified with light and will have perceived that their outlines are con- shadow: some parts are dark and others light. fused, and that they seem to tremble or vibrate The interpretation that is put on this variation rapidly. Precisely such movements are taking is, that the Moon, like the Earth, is composed place in the air above us, and these cause the of rocks of many different tints; that the large mountains on the moon to twinkle like a star. spaces I now indicate, and which used to be During two years, in which I took photographs called seas, are made up of a darker rock than of the Moon every night that she shone, only the volcanic southern regions. At the tip of three good nights occurred, and even on these the rod, the volcano Copernicus has ejected a there was some vibrating motion. Professor lava whiter than the plains over which it has Bond, of the Cambridge Observatory, said that flowed. Observe how far the stream running he had never in his lifetime seen a perfectly north has gone; let me give you a scale of faultless night. If, then, it were desired to con- miles: this picture is 12 feet in diameter; it vey to you by our former simile of a man walk-shows the Moon as she would appear to us if ing the difficulties of Moon photography, it would be necessary to superadd that the man was afflicted with St. Vitus's dance.

Besides all these obstacles others must be specified. A telescope of very large size is necessary in order that photographs may be procured with rapidity, and such an instrument is difficult to obtain. It must be either bought or made by the observer. In the latter case the time consumed in perfecting the lenses or mirrors is very great. I spent six years on my instrument, but had then the satisfaction of knowing that it was thoroughly adapted to its purpose. It has a mirror 15 inches in diameter, and a tube 124 feet long, and is mounted at Hastings on Hudson, 20 miles north of

A fac-simile of Dr. Draper's photograph of the Moon was published in Harper's Weekly for March 19, 1864.

we were 166 miles from her, instead of 240,000, as we now are. Every foot length in the picture is about 180 miles. You will see that the lava stream running north has gone not less than 600 or 800 miles.

I have said that this lava is running across a plain. Why do we not call it by the old name, a sea-the Sea of Showers? If you will look closely and reason a little, the cause will be apparent enough. If this dark spot were a sheet of water it would present a uniform grayish or greenish tint. But we see it diversified with mottlings of light and shade, bright points and streaks of white lava. It must be land.

* Here was exhibited an enlarged view of a photograph of the Moon. The picture was about 12 feet in diameter; the light and shade, craters, mountains, etc., were shown beautifully defined.

In the next place, we will examine the straight | points are seen apparently altogether disconor rugged side of the picture. On casting the nected from her. These are the tips of mounteye along this part it will at once be noticed ains, or the rims of craters, on which the sunthat it is irregular and seems to be thickly dot-light is falling while it does not reach their ted with depressions of a saucer shape. It is sometimes said that the Moon looks as if she had suffered from an attack of small-pox. What is the nature of these marks?

bases. On the Earth the Sun in rising illuminates first the peaks of mountains, and then the light gradually creeps down their sides until they are all lightened up. So it is in the Moon. If the photograph had been taken a little while later than it was many of these bright points on the edge would have disap

Let me observe that there are not on the Moon a large number of mountains, truly speaking—that is, ranges of projecting peaks. The best example of them is this range, the "Lu-peared, because this is a photograph of the nar Apennines;" they are perhaps 400 miles long at this part, and 15,000 feet high.

waning Moon; they were depicted just as the Sun was setting on them.

Why is it that the parts on the left hand of the picture are of so uniform a brightness, and do not show craters and peaks too? It is because the light is there falling perpendicularly on the surface and illuminating all parts uniformly. If a person were suspended in a balloon over the Earth, and the Sun were over

a mountain from the valleys around if similarly composed. But in the morning, when the Sun's rays strike the surface obliquely and the mountains cast a shadow, there would be no difficulty. The part of the Moon on the ex

You may ask how we know that one spot is a mountain, another a crater. It is by observing the direction in which the shadows are cast. The Moon does not shine by her own light, but is seen by light falling on her from the Sun and reflected to us. The Earth is just as bright to her as she is to us. When the Moon is at half, as she is represented in this photo-head, he would find difficulty in distinguishing graph, the light falls obliquely on the part we have called the rugged edge, just as at sunrise on the Earth. Every object that projects is bright on the side toward the light, and in shadow on the opposite side, while every excavation or pit is in just the reverse condition-treme left is here seen at mid-day, so to speak, bright on the side from the Sun, and dark on the side toward him. Bearing this in mind, let us investigate some of these spots in the Moon. The Sun is away toward the left hand; in the Apennines the bright side is toward the left, and the dark toward the right. They are therefore, according to our rule, projections. But in this crater the dark side is toward the left, and the bright toward the right. It must be a pit.

In this crater, named after Aristillus, you will observe a peculiarity common to many of the craters. It has in the centre a small bright dot, resulting from light falling on a conical mountain. This same central cone is seen in certain volcanic mountains on the Earth, as in Vesuvius for example. Any one who has ascended it will remember that the cone which now emits lava occasionally is surrounded at a distance by an old crater, just as if in the centre of a saucer a small pile of sand should be placed; the latter would represent the cone, 'while the rim of the saucer would be the wall of the crater. Here I point out another named after Eratosthenes; here another, etc.

The various craters in the Moon have been named after distinguished men; this one, for instance, is Copernicus, who revived the doctrine that the Sun is the centre of the Solar System; this after Kepler, the discoverer of three great astronomical laws; this after Tycho Brahe, the Dane; this after Plato, etc. The dark parts are named from imaginary qualities they were supposed to possess; this is the Sea of Showers, or Mare Imbrium; this the Oceanus Procellarum, or Ocean of Storms; this the Sea of Vapors.

that at the rugged edge at evening.*

We

And now what is to be said on the subject of Plurality of Worlds is about finished. have taken a glance at the celestial bodies, and shown that on one of them, a near neighbor, Mars, the conditions exist necessary to animated beings. From it we may extend the observation to some of the rest. I could not offer you positive proofs, but have indicated how strong the probabilities are of inhabitation. In all such investigations it is necessary to be very careful in drawing conclusions from what we may see. The senses alone often deceive us, and results derived from them must be corroborated by our reason. Many instances could be adduced in proof of this assertion, and none more striking than those in connection with the body whose description has occupied so much of this evening.

It is generally supposed that the rays proceeding from the Moon are so cold as to produce refrigeration in bodies exposed to them. This property has been a favorite subject of comparison with poets, as a thousand quotations concerning her cold, pale light would prove. In the old mythology the lack of warmth of Diana was typified by this body. But what

In the

In the cut on page 46 a part of the rugged edge of the Moon is shown. The drawing is from Professor Nichol's Cyclopedia. The reader will observe the long shadows cast by the mountain peaks and edges of craters. other cut, page 47, which is from a drawing by the eminent engineer James Nasmyth, a more full illumination of the surface is exhibited. It gives an admirable idea of the broken, volcanic nature of the surface of our satellite, and suggests at once the sterility and uninhabitability of such a place. But excellent as these drawings are they can convey but a faint idea of the beauty of the Moon as a telescopic object. The photograph, enlarged by the calciuma Along the extreme edge of the Moon many light, has more nearly the general effect.

one eye is still kept at the eye-piece of the telescope the other be opened, two moons are seen, a small one not as large as a pea, and another 6 or 8 times as great. By shutting first one eye and then the other, it can be shown that the small one is that seen by the naked eye. After repeating such an experiment several times the effect is permanent, the Moon looks always small, but if only once performed on going away from the telescope we again delude ourselves.

are the facts in the case? The Moon reflects to us a certain proportion of heat from the Sun, and by thermometers sufficiently delicate the amount may be measured. An ordinary mercurial thermometer fails entirely to show any rise, though the moonbeams be concentrated by ever so large a lens. But if two wires, one of bismuth and the other of antimony, be soldered together at the ends, an exceedingly slight warming at the junction will cause an electrical current to be developed. By appropriate contrivances we are able to measure In producing this photograph on the table, the strength of the current, and as it bears a 21 inches in diameter, a magnifying power of relation to the amount of heat employed, thus about 200 has been used, and yet it seems no measure that heat. A number of pairs of such larger than half the rising Moon. But why is metals soldered together is called a thermo- it then, if the size is the same in both cases, electric pile. By the thermo-electric pile that we do not see with the naked eye the craof a degree may be indicated. The moon-ters and cones and other parts as we see them beams warm us to about this extent. To be sure the amount is not great, but it is sufficient to overturn the idea of her cooling agency.

In another instance a deception of the eye is shown. When the moon is rising it is generally conceded that she is much larger than when near the zenith. She seems as large as a cart-wheel, while overhead the diameter is not greater than a plate. Any one who doubts this doubts the evidence of the senses. And yet measured with the telescope the size is seen to be the same on each occasion. Does not such a fact shake our confidence in the eye?

here. No one is apt to amuse himself with imagining the face of a man in the Moon depicted on this paper; his attention is too much occupied with a multiplicity of details far more interesting. Not much reasoning is required to satisfy the mind that the greater distinctness of parts must arise from the fact that the photograph is a magnified representation.

The Moon varies in her distance from the Earth considerably at different times. She should seem, therefore, on some occasions, much greater in size to us than on others. And yet who remarks the change in apparent diameter. A series of photographs taken on various occasions vary in size very materially, and bring this fact before us in a forcible manner. Yet the eye commits in this case a sin of omission.

the position of celestial bodies have to make a correction for this disturbance. It is generally supposed that we see in a straight line, but in looking at these bodies the light has reached the eye through a curved path.

A still more common deception which astronomers have to combat is that connected with the apparent size of the Moon. When it was stated a moment ago that overhead she seems as large as a plate, no dissent was ex- In yet another instance the unreliability of pressed, because almost every one feels con- the senses is shown when not corrected by reavinced that such is the fact from repeated ob- son. We see the Moon and Stars before they servation. But yet by two simple experiments have risen and after they have set. We never our faith in that can be altogether broken. see them in their true positions, except in the Many times the inquiry is made in my observa- rare case when they are directly overhead. tory, "How large do you take your photo-The refractive action of the air lifts them out graphs of the Moon in the telescope?" On of their places, and astronomers in measuring returning the answer that they are magnified 15 times by the instrument, and then showing a specimen about an inch and a half in diameter, persons either say, "This is smaller than the Moon," or else express their disbelief in a yet more marked manner by a silent dissent. The size of the Moon as seen by the naked eye is about that of a pepper-corn. Now that I know this to be the case she has lost her former magnitude to my eyes. In order to convince persons it is only needful to cause them to hold up such a photograph (about as large as a half dollar) at the distance of distinct vision, 10 inches, and then look at the Moon through it. At once her size dwindles away; we have established a standard of comparison, and see how great the deception was.

In another way any one who has a spy-glass mounted on a stand can convince himself of the same thing. If the instrument magnify only 6 or 8 times, on looking through it at the Moon, she seems to be smaller than to the naked eye, possibly not larger than a penny. But if while

A

In reasoning then on such a subject as that which has occupied us this evening, we are admonished not to let our senses and imagination carry us away. Do not speculate on the nature of beings on other spheres as some have done, and attribute to them a variety of qualities corresponding to their supposed surroundings. Do not, with Fontenelle, give to the inhabitants of the hot planets, Mercury and Venus, characteristics in an exaggerated degree like those possessed by the inhabitants of our warm climates, doubting not that Venus is the seat of an empire where ardent affection rules, while in Mercury the vivacity of the inhabitants is so great that it is the Insane Asylum of the Universe; from the coldness of Jupiter and Saturn imagining that they are peopled with phlegmatic and slow-moving inhabitants.

Do