Science and the Infinite by Sydney T. Klein (english books to improve english txt) 📖

background; the angle which the lines of sight, from each eye, make when they meet at the object, is called the angle of parallax, and the further the object is away the smaller that angle becomes; it is, in fact, the angle subtended, at the object, by the distance between the two eyes. As the object is brought nearer the eyes have to be inclined inwards to impinge on that object; the appreciation of distance then, in our sense of sight, is dependent upon our perception of the amount of inclination of those two lines of sight, and is therefore an acquired knowledge. The distance between the eyes is about 2-1/2 inches, and this is a very short base line upon which to estimate distance; in fact, without the help of perspective and known dimensions of surrounding objects, it is doubtful if anyone could by its means estimate distance beyond a few hundred yards. The object would, of course, also have to be an unknown one, as, otherwise, the converse of the above comes into play, and the distance could be estimated by the angle which the known diameter of the object subtends at the eye; but this necessitates the size of the object being known beforehand and the employment of perspective.

We can extend our perception of distances by, ourselves, moving from one place to another, gaining thereby a longer base line, and noting the displacement of projection of the object on a distant background; by that means, distance up to several miles can probably be appreciated. But, when we try to determine the distance of, say, the Moon (240,000 miles away), we are helpless, especially as we have no marked background, except in the case of occultations of the Sun or Stars. But the Astronomer at once comes to our aid; a distance of several miles is carefully measured on a level plane, and, by placing telescopes at the extremities of that known line, we can mark the inclination of those telescopes to each other when focussed upon a particular mountain peak on the moon; by this means we know the angle of parallax (180° less the sum of the two angles of inclination), and, from this and our known length of base line, we can calculate the distance. When however we go a step further and attempt to calculate the distance of the Sun (93,000,000 miles), we find our last base line again absolutely inadequate. But the astronomer helps us again; we now separate our two telescopic eyes by the whole diameter of the earth (7900 miles); this is accomplished by taking from the Equator two simultaneous observations of the Sun, at its rising and setting; for when the Sun is setting, at say the Equinox, it is at that moment rising at exactly the other side of the earth; the inclination of the two telescopes, directed to a certain point on the Sun, will now give the distance approximately, though even this base line is too short for exactitude. When however we attempt to go still further and try to ascertain the distance of stars, which are a million times further off than the Sun, such a base line is quite out of the question. How then can we get a base line for our telescopes longer than the whole width of the earth? The Astronomer again provides the means. The earth takes one year to complete its vast orbit round the sun, and the diameter of that path is 186,000,000 miles. This is made our new base line for separating our telescopes; an observation of a star is taken, say, to-day, and after waiting six months, to enable the earth to reach the other extremity of its vast orbit, another observation is taken, and yet it is found, as we shall see later on, that the distance of the nearest fixed star is so stupendous that even this base line, of 186,000,000 miles, shows absolutely no inclination between the two telescopes except in about a dozen cases, and even in those the angle of parallax, perceivable, is so minute that no reliable distance can be calculated; we can only say that the star is at least as far away as a certain distance, but it may be much farther.

Let us now try by other means to get a clearer insight into the subject of this View, by tracing Space to the utmost limit of human conception. I think the best method I can adopt will be to take you, in imagination, for a journey as far as is possible by means of the best instruments at our disposal.

We will start outwards from the Sun, and glance on our way at the worlds involved in the Solar System. Let us first understand what are the dimensions of our central Luminary. The distance of the Moon from the Earth is 240,000 miles, but the dimensions of the Sun are so great that, were the centre of the Sun placed where the centre of the Earth is, the surface of the Sun would not only extend as far as the Moon, but as far again on the other side, and that would give the radius only of the enormous circumference of the Sun; another way to understand its size is, to remember that, light travelling 186,000 miles per second, would actually take five seconds to go across its disc. Let us now start outward from this vast mass. The first world we meet is the little planet Mercury, only 3000 miles in diameter, revolving round the Sun at a distance of 36 million miles. We next come upon Venus, at a distance of 67 million miles. She is only 400 miles smaller in diameter than our Earth, and, with the dense atmosphere with which she is surrounded, animal and vegetable life similar to that on our Earth would be possible. Continuing our course, we arrive at our Earth, situated 93 million miles away from the Sun. Still speeding on, a further 50 million miles brings us to Mars, with a diameter of nearly 5000 miles, and accompanied by two miniature moons. The sight of this planet in a good instrument is most interesting. Ocean beds and continents are visible, and the telescope shows large tracts of snow, though not necessarily formed from water (perhaps carbonic dioxide), surrounding its polar regions, which increase considerably during the winter, and decrease during the summer seasons on that planet; but there are no canals! The fact that our largest and best telescopes failed to show these imaginary canals, was an insurmountable barrier to the advocates of these markings, but the "Canalites" made their contention ridiculous when they actually suggested that the reason for this failure to perceive them was that our telescopes were too large to see such small markings! How such a statement could have been made is incomprehensible on any supposition, as everybody knows that the whole use of size, or what is called aperture, in a telescope, is to help us to see more clearly small and faint markings.

The distances we now have to travel become so great that I shall not attempt to give them; you can, however, form an idea of the tremendous spaces we are traversing when you consider that each successive planet is nearly double as far from the Sun as the preceding one.

In the place where, by Bode's law, we should expect to have found the next world, we find a group of small planets, ranging in size from about 200 miles in diameter down to only a few hundred yards. They pass through nearly the same point once in each of their periods of revolution round the Sun, and it has been suggested that they are fragments of a great globe rent asunder by some mighty catastrophe; over 400 of these little worlds have been discovered and have received names, or are known under certain numbers.

We now continue our voyage over the next huge space and arrive at Jupiter, the largest and grandest of the planets. This world is more than 1000 times larger than our Earth, its circumference being actually greater than the distance from the Earth to the Moon. It has seven moons, and its year is about twelve times as long as ours. Pursuing our journey, we next come to Saturn. It is nearly as large as Jupiter, and has a huge ring of planetary matter revolving round it in addition to seven moons. Further and further we go, and the planets behind us are disappearing, and even the Sun is dwindling down to a mere speck; still we hurry on, and at last alight on another planet, Uranus, about sixty times larger than our Earth; we see moons in attendance, but they have scarcely any light to reflect; the Sun is only a star now; but we must hasten on deeper and deeper into space. We shall again, as formerly, have to go nearly as far beyond the last planet as that planet is from the Sun. The mind cannot grasp these huge distances. Still we travel on to the last planet, Neptune, revolving on its lonely orbit; sunk so deep into space that, though it rushes round the Sun at the rate of 22,000 miles per hour, it takes 164 of our years to complete one revolution. Now let us look back from this remote point. What do we see? One planet only, Uranus, is visible to the unaided eye; the giant planets, Jupiter and Saturn, have disappeared, and the Sun itself is now only a star; practically no heat, no light, all is darkness in this solitary world; the Sun is 1000 times smaller than we see it from the earth, and gives, therefore, only one-thousandth part of its heat and light. Thus far have we gone, and, standing there at the enormous distance of 3,000,000,000 miles from our starting-point, we can begin to comprehend the vast limits of the solar system; we can begin to understand the ways of this mighty family of planets and satellites. But let us not set up too small a standard whereby to measure the Infinity of Space. We shall find, as we go on, that this stupendous system is but an infinitesimal part of the whole universe.

Let us now look forward along the path we are to take. We are standing on the outermost part of our Solar System, and there is no other planet towards which we can wing our flight; but all around are multitudes of stars, some shining with a brightness almost equal to what our Sun appears to give forth at that great distance, others hardly visible, but the smallest telescope increases their number enormously, and presents to our mind the appalling phantom of immensity in all its terror, standing there to withstand our next great step. How are we to continue on our journey when our very senses seem paralysed by this obstruction, and even imagination is powerless from utter loneliness? One guide only is there to help us, the messenger which flits from star to star, universe to universe; Light it is which will help us to appreciate even these bottomless depths. Now, Light travels 186,000 miles per second, or 12 million miles every minute of time. It therefore takes only about four hours to traverse the huge distance between our Sun and Neptune, where we are now supposed to be standing; but to leap across the space separating us from the nearest star, it would require many years for Light, travelling at 186,000 miles every second of that time, to span the distance. There are, in fact, only fifteen stars in the whole heaven that could be reached, on the wings of Light, in sixteen years!

Let us use this to continue our