Rensselaer Union, Volume 8, Number 46, Rensselaer, Jasper County, 3 August 1876 — The Brilliant Meteor of July 8—Meteors in General. [ARTICLE]

The Brilliant Meteor of July 8—Meteors in General.

The visible flight of the meteor (seen from Chicago and many other Western points, on the evening of July 8), is estimated to have occupied about four seconds of time, which gives an average of twentytwo to twenty-three miles per second. When first seen, it was already moving with a diminished velocity, having passed through several hundred miles of highlyrarefied air, which continually retarded its motion; and that retardation was continued during and after the time the meteor was visible. When first seen, its relative velocity was not far from twentyfive hitles, and when it had passed beyond our atmosphere its relative velocity had diminished to considerably less than fifteen miles per second. This is equivalent to saving that its motion in space was reduced to zero. After it had left the neighborhood of the earth, the meteor was powerless to proceed farther, its vis viva having been destroyed by the passage through the upper air.

The body which had previously been revolving in space around the sun, perhaps for thousands of centuries, as independently as the earth itself, if not of so much consequence, was thus brought to a dead stop, as it were; and what then? The solar attraction, which had hitherto drawn it away continuously from a tangent to the momentary direction of its course, now operated without hindrance to draw the wanderer to his own bosom. At first it responded but slowly to the invitation, falling through only the ninth part of an inch m one second of time. But the motion is an accelerating one. It is now moving much more rapidly than that, and will continue to increase its speed till (and not until) after the lapse of sixty-six days from the date of its encounter with the earth, that meteor will plunge into the fervent embrace of the sun with a final velocity of nearly 879 miles per second We can calculate the time to a nicety, so that we could turn the telescope upon the sun at the instant of the concussion, but probably without being able to witness the catastrophe. It would require a very high magnifying power to render it visible at the vast distance of 92,000,000 miles, and the contact will recur at a point on the solar surface which will then be more than sixty de-| greesfrom the center of the dire —the earth having moved so far in her orbit during the time of the fall.

It is certainly possible that enough forward motion was left after the collision to permit the body to sweep around the sun in a very narrow orbit, instead of falling to him. In this case the aphelion point of the new orbit would be near the place in which the earth destroyed the former orbit, and the meteor might again make our acquaintance in the future. But it ip more probable that the meteor is now falling directly toward the sun. There is good reason to believe that many meteors and comets have been turned out of their former paths by the larger planets, and forced to revolve in new orbits, the aphelia of which lie near the path of the revolution-maker. How many been swallowed up by those planets, or hurled directly toward the sun, we cannot say—probably innumerable millions. It is probable that of all the meteors, large and small, .which come far enough within our atmosphere to be heated to self-luminosity, not more than one in thirty, perhaps not so many, avoid falling to the earth. So much heat is generated by the friction that nearly all the meteors explode (especially the smaller ones, and those which are not chiefly metallic in their composition), and the debris is scattered in all directions, the forward motion of most of the particles being destroyed by the explosion, and by the greater atmospheric resistance due to ificrease of surface in proportion to the mass of the particle. The fragments' fall to the earth, chiefly in the form of dust, which is literally ashes, being a product of combustion. Many of the meteors are so smail, probably* weighing no more than a single grain, tfyat they disappear in falling without exploding, being burnt out before they arrive within forty miles of the earth’s surface: If, however, the mass be large enough, and sufficiently cohesive, then it is not a difficult problem in mathematics

to calculate which way it will move, if we can know its original direction and rate of travel. We may illustrate by reference to the familiar fact that the earth attracts a stone dear her surface with a force capable of making it fall through sixteen feet in one second, sixty-four feet in two seconds, 144 feet in three seconds, and so on. From this, and knowing the size of the earth, we can calculate that in five her surface bends just about as- much as the stone would fall in one second. Therefore, if a meteor be moving near the earth’s surface, and parallel to it, with a velocity of less than five miles per second, it will fall to the earth; If its velocity be greater than five miles, the earth’s attraction will not bend the meteor downward so rapidly a 3 the earth’s surface curves, and the meteor will recede from the earth. In the present case, the meteor was trav*. eling far mere rapidly than this limit when moving parallel with the surface, therefore passed out again into space. The principle above stated is applicable in every case, though the calculation may be sometimes a rather tedious one. The friction of the atmosphere made the meteor incandescent; and this can also be made the subject of calculation —almost as close as we please. We know that the force needed to stop a velocity of 228 feet per second is equal to that required to raise the temperature of an equal weight of water, one degree Fahrenheit; and, as in the other case, the force required increases with the square of the velocity. An ordinary body, when at the temperature of about 2,600 degrees above the actual zero, glows with a white heat. Calculating on these figures as a basis we find that the conversion of a velocity of two miles per second into heat, gives the equivalent of incandescence. In the case of this meteor we have the motion retarded to the extent of some twenty miles per second, which developed not far from 26,000 degrees of heat. In a large body the friction must heat the surface much more rapidly than the interior, which causes unequal expansion, and a breaking up of the exterior, as the surface of a rock is pulverized by frost. These incandescent particles were left behind—swept off, as the wind sweeps off the dust from the rock, —and formed the visible trail of the meteor, which “lasted’’till those particles Bad cooled down below the incandescent point, by radiation into the surrounding air. The tremendous eflect of this lieat-making “destruction” of motion may be interred from the fact that some observers saw that incandescent trail —witnessed the continued luminosity of the separated particles, —for fully forty-five minutes, and one or two saw it for even a longer period; though in the intense cold of the upper air the cooling process must be much more rapid than at any temperature we experience on this earth’s surface. [Some of the debris may be driven off in lumps, and be projected some distance from the line over which the principal mass travels. One such lump is reported to have descended at South Bend.] The past two weeks have been unusually prolific in brilliant meteors. One was seen in the East the (Sunday) night after the appearance of the one which excited so much interest in the West—and the published reports indicated that it was almost equally brilliant. Several others have been seen in this section—from all of which some persons have inferred that “ there is something the matter.” As they understand the conclusion, they are altogether wrong, and just as foolish as the seafarer who should infer that some dire saw a few larger fish than ordinary playing around the sides of his ship. Kepler suggested that there may be as many comets in the heavens as there are fishes in the ocean, and modem soience confirms the idea—associating meteoric bodies with the comets. The universe is swarming with matter, as our world is teeming with life; and it is only under unusual conditions that we can become cognizant of the one, just as we are obliged to employ the microscope in order to 'perceive the existence of the other fact. The occurrence of two or three unusually brilliant meteoric exhibitions may be of more interest to us, but is of no more importance in the economy of Nature, than the falling of a few extraordinarily large snow-flakes during a storm. The idea that they have increased the temperature of “ the heated term” is equally ridiculous with the fancy that the rushing of the meteor of July 8 was heard by those who witnessed its passage. Heat is chiefly communicated upwards; and the sound of the meteor would occupy about five minutes in traveling to our ears through a distance of sixty-five miles. — Chicago Tribune.