OBJECTS, PLEASURES, AND ADVANTAGES OF SCIENCE. xiii 



the small collections of a few visible stars called Constellation* ; nay, what appears to the naked eye only a 

 light cloud, as the Milky Way, when viewed through the telescope, proves to be an assemblage of innu- 

 merable Fixed Stan, each of them ia all likelihood a sun and a system like the rest, though at an 

 immeasurable distance from ours. 



The size, and motions, and distances of the heavenly bodies are such as to exceed the power of 

 ordinary imagination, from any comparison with the smaller things we see around us. The Earth's 

 diameter is nearly 8,000 miles in length ; but the Sun's is above 880,000 miles, and the bulk of the Sun is 

 above 1,300,000 times greater than that of the Earth. The planet Jupiter, which looks like a mere speck, 

 from his vast distance, is nearly 1,300 times larger than the Earth. Our distance from the Sun is above 95 

 millions of miles ; but Jupiter is 490 millions, and Saturn 900 millions of miles distant from the Sun. The 

 rate at which the Earth moves round the Sun is 68,000 miles an hour, or 140 times swifter than the 

 motion of a cannon-ball ; and the planet Mercury, the nearest to the Sun, moves still quicker, nearly 

 110,000 miles an hour. We, upon the Earth's surface, besides being carried round the Sun, move rouud 

 the Uarth's axis by the rotatory or spinning motion which it has ; so that every 24 hours we move in this 

 manner near 24,000 miles, besides moving round the Sun above 1,600,000 miles. These motions and 

 distances, however, prodigious as they are, seem as nothing compared to those of the comets, one of which, 

 when farthest from the Sun, is 11,200 millions of miles from him ; and, when nearest the Sun, flies at the 

 amazing rate of 8SO.OOO miles an hour. Sir Isaac Newton calculated its heat at 2,000 times that of 

 red-hot iron ; and that it would take thousands of years to cool. But the distance of the Fixed Stars is 

 yet more vast : they have been supposed to be 400,000 times farther from us than we are from the Sun, that 

 is 38 millions of millions of miles ; so that a cannon-ball would take nearly nine millions of years to reach 

 one of them, supposing there was nothing to hinder it from pursuing its course thither. As light takes 

 about eight minutes and a quarter to reach us from the Sun, it would be above six years in coining from one 

 of those stars; but the calculations of later astronomers prove some stars to be so far distant, that 

 their light must take centuries before it can reach ua ; so that every particle of light which enters our 

 eye* left the star it comes from three or four hundred years ago. 



Astronomen have, by means of their excellent glasses, aided by Geometry and calculations, been 

 able to observe not only stars, planets, and their satellites, invisible to the naked eye, but to measure the 

 height of mountains in the Moon, by observations of the shadows which those eminences cast on her surface ; 

 the angles of these shadows being taken for that purpose. 



The table.", which they hare by the like means been enabled to form of the heaTenly motions, are of 

 use in navigation. By means of the eclipses of Jupiter's satellites, and by the tables of the Moon's 

 motions, we can ascertain the position of a ship at sea; for the observation of the Sun's height at mid-day 

 gives the latitude of the place ; that is, its distance from the equinoctial or equator, the line passing through 

 the middle of the Earth's surface equally distant from both poles ; and these tables, with the observations 

 of the satellites, or moons, give the distance east and west of the observatory for which the tables are 

 calculated called the longitude of the place: consequently the mariner can thus tell, nearly, in what part of 

 the ocean be is, how far he has sailed from his port of departure, and how far he must sail, and in what 

 direction, to gain tho port of his destination. Tho advantage of this knowledge is therefore manifest in 

 the common affairs of life ; but it sinks into insignificance compared with the vast extent of those views 

 which the contemplations of the science afford, of numberless worlds filling the immensity of space, and 

 all kept in their places, and adjusted in their prodigious motions by the same simple principle, under the 

 guidance of an all-wise and all-powerful Creator. 



We hare been considering the application of Dynamics to the motions of the heavenly bodies, which 

 forms the science of Phyiical Aitronomy. The application of Dynamics to the calculation, production, and 

 direction of motion, forms the science of Mechanic*, sometimes called Practical Mechanic*, to distinguish it 

 from the more general use of the word, which comprehends every thing that relates to motion and force. 

 The fundamental principle of the science, upon which it mainly depends, flows immediately from a property 

 of the circle already mentioned, and which, perhaps, appeared at the moment of little value, that tho 

 lengths of circles are in proportion to their diameters. Observe how upon this simple truth nearly tho 

 whole of those contrivances are built by which the power of man ia increased as far as solid matter assists 

 him in extending it; and nearly the whole of those doctrines, too, by which he is enabled to explain the 

 voluntary motions of animals, as far as these depend upon their own bodies. There can be nothing 

 more instructive in showing the importance and fruitfulness of scientific truths, however trivial and forbid- 

 ding they may at first sight appear. For it is an immediate consequence of this property of the circle, 

 that if a rod of iron, or beam of wood, or any other solid material, be placed on a point, or pivot, so that 

 it may move as the arms of a balance do round its centre, or a see-saw board does round its prop, the 

 two ends will go through parts of circles, each proportioned to that arm of the beam to which it belongs : 

 the two circles will be equal if the pivot be in the centre or middle point of the beam ; but if it be nearer 

 one end tlian 4ho other, say three times, that end will go through a circular space, or arch, three times 

 shorter than the circular space tho other end goes through in the same time. If, then, tho end of the 



