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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![mighty career in the heavens 7 This letter idea has been long entertained. It was however to the illustrious Herschel—to whom I have had occasion eo often to refer—that we owe the confirmation of this great truth. His idea was this, and you will aee at once that his mode of lighting upon the great fact was remarkably simple: He said, If our Sun is in motion, how shall we ascertain the fact ? We <can not ascertain it by the motion of the Sun him- self, because we, partaking of his motion, would not have it in our power to ascertain that motion inas- much as we are going on in the same path. The only mode by which it could be deduced was this .- If the sun were moving through the heavens, the stars around him would seem to he altering their position. Suppose for instance, to illustrate Her- echel's idea, that there is a cluster of trees before me and another cluster behind me. Now if I were to move from one toward the other, the cluster which I approach would seem to be opening up, while the cluster from which I was departing would seem to be undergoing the opposite change—closing sin. Now, Herscbel, upon comparing the positions of the stars with their positions as laid down in the old catalogues.discovered that justexactly such changes were going on among them. In the direction of the constellation Hercules the stars appeared to boopen- ing out, while the stars in the opposite part of the heavens seemed to be getting closer to each other. Now, said he, Is not this all I could expect to see if the Sun was actually moving through the heavens'/ Accordingly he was daring enough to infer that this was the case and he said our great Sun is mov- ing on with all his satelites toward the constella- tion Hercules. Again hesaid, If it be true that the Sun issweeping through space, then it will be found that the stars in all parts of the heavens are chang- ing ; not merely those in the region toward which the Sun is moving and from whicn he is departing, but sideways over all the heavens will distinct changes among the stars be apparent. To illus- trate again. Suppose for instance that I was mov- ing through this room. All the objects in it, on either aide of me. would appear to be moving backward. So has it been found to be with regard to the whole mass of the stars. They all present the phe- nomena as if they were being passed by the Sun. Since Herschel's time these motions have been scanned with the utmost precision, and his conjee- Cure has been most thoroughly confirmed. There ^cannot, then, be a doubt that our great Sun, carry- ing all his planets with him, is sweeping in a mighty cycle through the skies. (Applause.) These general considerations, however, have re- ference only to the general direction and motion of the Sun, which is probably enough for the purpose I had immediately in view ; but curiosity will de- mand if we know aught of his velocity or the na- ture of his course ? Until comparatively recently it was considered impossible even for Astronomical instruments, powerful as they were, to solve the g;reat problem of the 8ideriel parallax—t measure -quantities so small as to determine the distances of the Fixed Stars from us. This, however, has been at last accomplished with regard to the star Gl •Cygni. The actual distance of this star has been ascertained. It is 670,000 times farther removed from us than the Sun, and our distance from the Sun is, speaking in round numbers, one hundred millions of miles (100,000,000). This distance is so great that light, which moves at the rate of two hundred thousand miles (200.000) per second, would take ten years to travel from that remote orb to the -Earth. Now this star 61 Cygni has a very remarkable proper motion, moving through a very considerable :space in the heavens every year. Now, since we know the actual distance of this star from as, and the quantity it is moving through the sky every year, we can convert that motion into miles and can thus ascertain how many miles it moves in a year. Now the question is, to what is this motion due, to the motion of the star or the motion of the Sun? Note the problem. The star is seeming to move every year through the sky, and now what causes this apparent motion ? We find the star is moving exactly in the direction it would appear to move if Us motion were owing to the motion of the Sun. We are inclined, therefore, to infer that the motion does not belong to the star, but to the Sun, and on this hypothesis we can compute the Sun's rate of motion, which is six times greater than that of the Earth in its motion round the Sun. If this, then, is at all characteristic of the amount of activity pervading the whole of our Stellar Uni- verse, although the skies will remain fixed so long as the human race will endure, this motion will be sufficient, within the endless cycles of time, com- pletely to cRange the aspect of our heavens. One can go forward, in imagination, to the time when ihe Constellations that now shine so brightly o'er ua shall be rolled away to some remote confine of space, and their places be occupied by other suns as bright and beautiful as they. If we are going toward this star 61 Cygni at the rate of four hundred thousand (400,000) miles per hour, we will reach the extremity of our Stellar Cluster in about two hundred millions of years! (200,000,000.) These periods may seem incompre- hensible. They indeed seem vast compared with human annals, but they are brief when laid beside the annals of our Globe. If Geology is not the sheerest fable—if we are not to return to the old conceptions, that the rocks with their entombed creatures have been laid down there purposely as the most mocking of enigmas—enigmas that seem to have meaning and yet have none—then during the vastest of the periods of which we have been speaking, our chief existing mountains were in be- ing, rearing their peaks toward different constella- tions and surviving in their littleness and fragility even these immense transitions. Extend now what seems true of the Sun to his other associated orbs and where is the repose—where the stability of our Heavens ! Because those very stars which shine on us, also shone over the Chaldeans; we spoke of their changeless rest, of their arrangements as being eternal. Alas! no, neither Space nor Time are the- aters of repose, and even our most stable existences are the seats and subjects of activities and ever revolving change, whose ultimate object is known to God alone. It seems, then, ladies and gentlemen, as far as we can judge from the aspects of the bodies around us, that we may consider our great cluster as being in ceaseless activity ; and that, therefore, those other clusters whose character I intend to bring be- fore you, are subject to something of the same des- tiny. If this is the case, how little wonderful is it that their shapes seem so capricious. There is nothing relative to them that is entitled to the name of stability, and we can view them only as exhibiting to us the phases of the successive steps of an immense progression. The kind of know- ledge that we can alone have with respect to them, even should they be watched during the entire ex- istence of the human race, is something like what we would learn concerning the terrestrial arrange- ment around us, if our knowledge were gained from a single glance of the eye, which was thenshut again forever. [Applause.] No more, probably, than so passing a glance will man ever attain con- cerning the destiny of these nebula?. I shall venture no farther amid these immensi-](https://iiif.wellcomecollection.org/image/b21143821_0014.jp2/full/800%2C/0/default.jpg)
