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do not disappear again by degrees, like a body that is gradually melted down in a furnace. But there is another consideration too, which natuTally occurs : pray what becomes of all this vast quantity of matter after it is reduced to light ? Is it ever colleaed again into solid bodies; or is it for ever lost and dissipated, after it has made its journey from the sun to the objce it illuminates ? It is somewhat strange, that of all that immense quantity of matter poured down on us during the day, that pervades and fills the whole universe; the moment we are deprived of the luminous body, the whole of it, in an instant, seems to be annihilated : in short, there are a number of difficulties attending the common received doctrine of light; nor do I think there is any point in natural philosophy the solution of which is less satisfactory. If we suppose every say to be a stream of particles of matter, darting from the luminous body, how can we conceive that these streams may be interfected and pierced by other streams of the same matter ten thousand thousand different ways, without causing the least confusion either to the one or the other? for in a clear night we see distinctly any particular star that we look at, although the rays coming from that star to our eye is pierced for millions of miles before it reaches us, by millions of streams of the same rays, from every other fun and star in the universe. Now suppose, in any other matter that we know of, and one would imagine there
ought at least to be some sort of analogy ; sup. pose, I fay, we fhould only attempt to make two streams pals one another; water, for instance, or air, one of the purest and the most fluid substances we are acquainted with, we find it totally impossible. The iwo streams will mutually interrupt and incommode one another, and the strongest will ever carry off the weakest into its own dire&ion; but if a stream of light is hit by ten thoufand other ftreams, moving at the rate of ten millions of miles in a minute, it is not even bent by the impression, nor in the smallest degree diverted from its course ; but reaches us with the fame precision and regularity, as if nothing had interfered with it. Besides, on the supposition that light is real particles of matter moving from the sun to ihe earth, in the space of seven minutes, how comes it to pass, that with all this wonderful velocity, there seems to be no moinentum ! for it communicates motion to no body. that obstruas its paffage, and no body whatever is removed by the percussion. Supposing we had never heard of this discovery, and were at once to be told of a current of matter flying at the rate of ten millions of miles in a minute, and so large as to cover one half of our globe, would we not imagine that the earth must instantly be torn to pieces by it, or carried off with the most incredible velocity ! It will be obje&ted, that the extreme minuteness of the particles of light prevents it from having any such effect; but as these particles are in such quantity,
and so close to each other as to cover the surface of every body that is opposed to them, and entirely to fill up that vast space betwixt the earth and the sun, this objection I should think in a great measure falls to the ground. The particles of air and of water are likewise extremely minute, and a small quantity of these will produce little or no effect, but increase their number, and only give them the millionth part of the velocity that is ascribed to a ray of light, and no force whatever could be able to withstand them.
Adieu. I have unwarily run myself into the very deeps of philosophy ; and find it rather difficult to struggle out again. I ask your pardon, and promise, if possible, for the future, to steer quite clear of them. I am sure, whatever this comet may be to the universe, it has been an ignis fatuus to me ; for it has led me strangely out of my road, and bewildered me amongst rocks and quicksands, where I was like to stick fifty times.
I have forgot whether or not you are a rigid Newtonian; if you are, I believe I had better recant in time, for fear of accidents. I know this is a very tender point ; and have seen many of those gentlemen, who are good christians too, that can bear with much more temper to hear the divinity of our Saviour called in question, than that of Sir Isaac ; and look on a Cartesian or a Ptolomcan, as a worle species of infidel than an atheist.
I remember, when I was at college, to have seen a heretic to their doctrine of gravity, very suddenly converted by being tossed in a blanket; and another, who denied the law of centripetal and centrifugal forces, foon brought to assent, from having the demonstration made upon his shoulders, by a stone whirled at the end of a string.
These are powerful arguments, and it is difficult to withstand them. I cry you mercy. I am without reach of you at present, and you are heartily welcome to wreak your vengeance on
L E T T E R
Palermo, July 6th.
MANY of the churches here are extremely rich and magnificent. The cathedral (or, as they call it, Madre Chiesa) is a venerable Gothic building, and of a large size; it is supported within by eighty columns of Oriental granate, and divided into a great number of chapels, fome of which are extremely rich, particularly that of St. Rofolia, the patroness of Palermo, who is held in greater veneration here, than all the persons of the Trinity; and, which is still much more than even the Virgin Mary herself. The relics of the faint are preserved in a large box of silver, curiously wrought, and enriched with precious stones. They perform many miracles, and are looked upon as the greatest treasure of the city. They are esteemed the most effe&tual remedy against the plague, and have often preserved them from that fatal distemper. The saint gained so much credit, in faving them from the last plague of Messina, although it was at two hundred miles distance, that they have, out of gratitude, ere&ted a noble monument to her. St. Agatha did as much for Catania, but that city has not been so generous to her. The other riches of this church confiit