were seen.

ward. Now, if the paths of all had been projected backwards, they would have all intersected in one region, and that region the one in which the most foreshortened ones So decidedly did this fact come out, that there were moments in which the meteors belted the sky like the meridians on a terrestrial globe, the pole of the globe being represented by a point in the constellation Leo. In fact, they all seemed to radiate from that point, and radiant-point is precisely the name given to it by astronomers. Now the longitude of this point is 142° or thereabout!

306. The apparent radiation from this point is an effect of perspective, and hence we gather that the paths of the meteors are parallel, or nearly so, and that the meteors themselves are all travelling in straight lines from that point.

307. Here, then, is proof positive enough that the meteoric hail was fairly directed against, and as fairly met by, the Earth. Now here another set of considerations comes in. Suppose, for instance, we were situated in the radiant point, and could see exactly the countries which occupied the hemisphere of our planet facing the meteors, at the moments our planet entered the shower, when it was in its midst, and when it emerged again. In consequence of the Earth's rotation, and as the shower can of course only fall on the hemisphere of the Earth most forward at the time, the places at which the shower is central, rising, and setting, so to speak, will be constantly varying. In fact, each spectator is carried round by the Earth's rotation, and enters about midnight the front hemisphere of the Earth—the one which is exposed to the meteoric hail. We know therefore, again to take an instance from the last display, that as the shower did not last long into the morning, the time of maximum for the whole Earth was certainly not later than that observed at Greenwich; but

we do not know that it was not considerably carlier. Had the actual number of meteors encountered by the Earth remained the same, the apparent number would have increased from midnight to 6 A.M.; as at 6 we should have been nearly in the middle of the front side of the Earth on which they would be showering.

308. By careful observations of the radiant-point it has been determined that the orbit of each member of the November star-shower, and therefore of the whole mass, is an ellipse with its perihelion lying on the Earth's orbit, and its aphelion point lying just beyond the orbit of Uranus; that its inclination to the plane of the ecliptic is 17°; and that the direction of the motion of the meteors is retrograde.

309. Up to the present time 56 such radiant-points, which possibly indicate 56 other similar groups moving round the Sun in cometary or planetary orbits, have been determined. The meteors of particular showers vary in their distinctive characters, some being larger and brighter than others, some whiter, some more ruddy than others, some swifter, and drawing after them more persistent trains than those of other showers.

LESSON XXV.-LUMINOUS METEORS (continued). CAUSE OF THE PHENOMENA OF METEORS. ORBITS OF SHOOTING STARS. DETONATING METEORS. METEORITES THEIR CLASSIFICATION. FALLS. CHEMICAL

AND PHYSICAL CONSTITUTION.

310. Now let us take the case of a single meteor entering our atmosphere. Why do we get such a brilliant appearance? In the first place, we have the Earth travelling at

the rate of 1,000 miles an hour, plunging into a mass of bodies whose velocity is at first equal to its own, and is then increased to 1,200 miles a minute by the Earth's attraction. The particle then enters our atmosphere at the rate of 30 miles a second; its motion is arrested by the friction of that atmosphere, which puts a break on it, and as the wheel of a tender gets hot under the same circumstances, and as a cannon-ball gets hot when the target impedes its further flight, so does the meteoric particle get hot. So hot does it get that, at last, as great heat is always accompanied by light, we see it: it becomes vaporized, and leaves a train of luminous vapour behind it.

311. It would seem that all the particles which compose the November shower are small: it has been estimated that some of them weigh but two grains. They begin to burn at a height of 74 miles, and are burnt up and disappear at a height of 54 miles; the average length of their visible paths being 42 miles. It is supposed that the November-shower meteors are composed of more easily destructible or of more inflammable materials than aërolitic bodies.

312. What has been said about the appearance of the November meteors applies to the other star-showers, notably to the August and April ones, the meteors of which also travel round the Sun in cometary orbits; in fact, there is reason to believe that three bodies, which were observed and recorded as comets, are really nothing but meteors, and belong one to the November, one to the August, and the other to the April group. This discovery, however, is so recent and so unexpected, and so much has to be done before we can thoroughly understand it, that in this little book it will be sufficient to state it merely.

313. In the case of the November and August meteors and shooting-stars generally, the mass is so small that it

is entirely changed into vapour and disappears without noise. There are other classes of meteoric bodies, however, with much more striking effects. At times meteors of great brilliancy are heard to explode with great noise these are called detonating meteors. On Nov. 15, 1859, a meteor of this class passed over New Jersey; it was visible in the full sunlight, and was followed by a series

Fig. 21.-Fire-ball, as observed in a telescope.

of terrific explosions, which were compared to the discharge of a thousand cannons. * Other meteors are so large that they reach the Earth before complete vaporization takes place, and we then get what is called a fall of meteoric irons, or meteoric stones, often accompanied by loud explosions.

314. Meteorites is the name given to those masses which, owing to their size, resist the action of the atmosphere, and actually complete their fall to the Earth. They are divided into aërolites, or meteoric stones; aërosiderites, or meteoric iron; and aërosiderolites, which includes the intervening varieties.

315. We do not know whether these meteors which Occasionally appear, and which are therefore called

* Professor Loomis.