Views of astronomy : seven lectures delivered before the Mercantile Library Association of New York in the months of January and February, 1848 / by J.P. Nichol ; reported for the New-York Tribune by Oliver Dyer.
- John Pringle Nichol
- Date:
- 1848
Licence: Public Domain Mark
Credit: Views of astronomy : seven lectures delivered before the Mercantile Library Association of New York in the months of January and February, 1848 / by J.P. Nichol ; reported for the New-York Tribune by Oliver Dyer. Source: Wellcome Collection.
Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)
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![other planets are more or less obscured by clouds floating in their atmospheres. Venus, for instance, although so near us, has such a heavy atmosphere constantly surcharged with clouds that our knowl- edge of the orb is doubtful; while Mars, although much farther from the Earth, is, owing to the va- riety of its atmosphere and its freedom from clouds, seen with singular distinctness. The Moon, as before remarked, having none of these obstruc- tions, appears clear and distinct. Beside, it is com- paratively very near the E arth—being only 240,000 miles from us, a distance which, astronomically speaking, is but a mere unit. Now taking into account what the Telescope can do, the Moon is brought very near us. A nine-inch Telescope, with a magnifying power of a thousand times which I for some time used, brought, as you can readily calculate, the orb within two hundred and forty miles of me. A Telescope with a magnifying power of three thousand times would bring it with- in eighty miles, and by applying a power of ten thousand, which might be done under favorable circumstances, this Luminary would be brought within the small distance of twenty-four miles ! The audience must not compare observing the Moon at this distance of twenty-four miles with viewing an object located on the Earth, at the same distance, for the view of the Earthly object would be obstructed by the lowest and densest portion of our atmosphere ; but it should be com- pared with the view we would have of an object situated directly above us at the bight of twenty four miles, when the vision would be much less affected by the atmosphere intervening, as it would be of the the clearest and best quality. I hope the audience will not take such a view of the matter as a gentleman did who on hearing me state that we could go within eighty miles of the Moon, waited on me afterward in troubled wonder, asking why we did not skip over the intervening space and go out to it altogether ? (Laughter.) Such are the circumstances with which we ap- proach the examination of the Moon. In posses- sion of these facilities, then, and with the foregoing object in view, let us examine with attention the up heavals which this globe [the Moon] presents: and we find them divided into three distinct classes or orders. 1 will just mention shortly, before proceeding to the description of these mountains, the means by which we ascertain their character and elevation. This is effected by measuring the shadows cast by them upon the Moon's surface. To illustrate : You observe that this pitcher casts a shadow of a cer- tain length. Now as I raise this light the shadow as the light arrives exactly over the object, it casts no shadow at all, and as the light continues to pass on the shadow begins to appear on the opposite side of the pitcher, and it continues to grow longer and longer as the light descends. We observe the relative positions of the Sun and the Earth. We mark the extremities of the long deep shadows cast by those elevations on the Moon's surface, and we find that as the Sun mounts higher and higher in the heavens, these shadows gradually recede to- ward the bases of the mountains: and when the Sun arrives at the zenith the shadows entirely dis- appear; bat by-and-by, as our majestic Luminary sinks to his bed in the West, the shadows come creeping out on the opposite side of the elevations, and we, by watching thus their movements, are enabled to ascertain with mathematical accuracy the character and hight of these Luuar mountains. There is no exaggeration in respect to our ability to measure hights and distances on the Moon. The shadows on the Moon are not like shadows on the Earth. They are black as midnight, and as clearly defined as form can be. Thus are these results re- liable, and in truth we are at present better ac- quainted with the structure of one side of the Moon than with anv hemisphere of our own globe. There are three classes of Lunar mountains.— The first class consists of isolated, separate, dis- tinct mountains of a very curious character. The distinguishing characteristic of these mountains is this : they start up from a plain quite suddenly.— On the Earth, it is well known that mountains gen- erally go in ranges or groups, but we find these isolated Lunar mountains standing up entirely apart —never haviDg been connected with any range.— Here is one [the lecturer here pointed to a splendid telescopic map of the Moon] named Pico, which is 9,000 feet high. This mountain has the form of an immense sugar-loaf; and if the audience can ima- gine a fairly-proportioned sugar-loaf 9,000 feet in hight, and themselves situated above it so as to be able to look down upon its apex, they will have an approximate idea of the appearance of Pico. There are many other mountains of a similar description scattered over the Moon's surface, and these moun- tains not only stand apart from each other, but, what is still more remarkable, the plains on which they stand are but slightly disturbed. How singu- lar, then, the influence that shot these mountains up 9,000 feet and yet scarcely disturbed the plain in their immediate neighborhood. The second class of Lunar elevations consists of mountain ranges. Now this is the principal fea- ture of the mountains upon Earth. They are rarely found associated in any other manner than in vast ranges. This phenomenon is also found in the Moon, but there it is the exception ; only two prin- cipal ranges are found and these appear to have been originally one range. One is called the Appenines. It is so well seen that just as the line of light is passing through the Moon you will think it is, generally speaking, a crack in its surface, but a telescope of ordinary power will at once manifest it to be a range of mountains. Now the Lunar Appenines may be compared with the loftiest ranges of mountains upon Earth. It is 18,000 feet high, and there is another range still higher—rising 25,000 feet above its base. In this feature, then, the Moon corres- ponds with the Earth, but with this difference.— What is the rule on the Earth is the exception, on the Moon. There is, however, another very remarkable fea- ture in which these ranges in the Moon correspond with Terrestial ranges. We find that on one side the mountains are quite steep, descending precipi- grows less and less, till at length you perceive that, ^tously, while on the other side they slope away through an extensive highland. Now this very re- markable law holds also with respect to ourTerres- tial ranges. It is not universal but is so general that some of our Geologists have assumed it as mainly in- dicative of the cause that has up-heaved our moun- tains. The Himmalaya mountains present this fea- ture most strikingly. On the South side they are bold and precipitous, while on the North they shelve gradually away, extending in picturesque grandeur over many a mile of mingled mountain, valley, gentle declivity and rolling plain, till at last they slope gently down and are lost in the level earth. So, too, the Andes exhibit this feature. It is a fact too remarkable to be considered accidental, and assuredly the cause which produced it upon the earth Earth must be similar in Nature to what evolved it in the Moon. Now our physical Geogra- phers have usually been disposed to attribute the Terrestial phenomenon to the action of great floods or currents of water originating in different ways. And it seems no inadequate illustration of the ben-](https://iiif.wellcomecollection.org/image/b21143821_0036.jp2/full/800%2C/0/default.jpg)
