parts was thirty times as broad, stretched through the celestial spaces to the enormous distance of one hundred and seventy millions of miles, or about the whole size of the orbit of the earth. Nor were its motions less singular. Unlike any globe connected with the sun, it did not move in a continuous curve, which, like the circle or ellipse, re-enters into itself, and thus constitutes, to the body that has adopted it, a fixed, however eccentric home; but spying our luminary afar off, as it lay amid those outer abysses, it approached along the arm of a hyperbola, rushed across the orderly orbits of our system into closest neighborhood with the sun, being at that time apart from him only by a seventh part of our distance from the moon, and, defying his attraction, by force of its own enormous velocity, which then was nothing less, in one part of its mass, than one third of the velocity of light, it entered on the other divergent arm of its course, and sped toward new immensities.

"It was when retiring that this unexpected visitant was seen for a brief period in Europe. In the course of its approach it must have passed between us and the sun, causing a cometic eclipse, and, in so far, an interception of his heating rays; but that occurred during our night.

"And now, what is to be made of this extraordinary apparition? what is its nature? what its relations to our system? and what new revelation does it bring concerning the structure of the universe? Its relations with our system appear to have been few and transitory; and in this it resembles the probable millions of such masses, that have, since observation began, crossed the planetary orbits toward the sun, and, after bending round him, gone in pursuit of some other fixed star. No more than three are known to belong, properly speaking, to the scheme dependant on our luminary-Encke's, Biela's, and Halley's; but though these do revolve around him in fixed periods, the circumstance must be regarded in the light of an accident, their orbits being wholly unlike any other, and having little assurance of stability; for as they cross the planetary paths, every one of them may yet undergo the fate of Lexell's, which, by the action of Jupiter, was first twisted from its diverging orbit into a comparatively short ellipse; and then, after making two consecutive revolutions around the sun, so that it might have begun to deem itself a denizen, was, by the same planet twisted back again, and sent off, never to revisit us, away to the chill abysses! Strange objects, with homes so undefined— flying from star to star-twisting and winding through tortuous courses, until, perhaps, no depth of that infinite has been untraversed! What, then, is it your destiny to tell us? To what new page of that infinite book are you an index? We missed, indeed, only very narrowly, an opportunity of information which might have been not the most convenient; for the earth escaped being involved in the huge tail of our recent visiter, merely by being fourteen days behind it. For one, I should have had no apprehension, even in that case, of the realization of geological romances, viz., of our equator being turned to the pole, and the pole to the equator-the ocean, meanwhile, leaping from its ancient bed. But if that mist, thin though it was, had, with its next to inconceivable swiftness, brushed across our globe, certainly strange tumults must have occurred in the atmosphere; and probably no agreeable modification of the breathing medium of organic beings. Right, certainly, to be most curious about comets; but prudent, withal, to inquire concerning them from a greater distance than that: although one night in November, 1837, I cannot be persuaded that the earth did not venture on a similar, but comparatively small experiment. It was when our globe passed from the peaceful vacant spaces into that mysterious meteor region. The sky became inflamed and red as blood; coruscations, like aurodarted across it; not as usual, streaming from one district, but shifting constantly, and sweeping the whole heavens."

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In the year 1844* two comets appeared, the first of which was seen in the month of July. It was described to have a bright white color-that its tail was turned from the earth so as not to be visible to us. Stars of very small magnitude were visible through its body, and its light was so strong that it was said to be easily detected in the heavens, in Europe, during the bright sunsets of July. A drawing of this comet, obtained at the Royal Observatory, Greenwich, is annexed.

The second comet of 1844 was seen in the month of September. It was observed at Kensington, by Sir James South, on the evening of the 15th. In the course of that month a drawing was obtained of it by the assistance of Sir

The following note is annexed to the last edition of Nichol's Solar System, relative to one of the comets of 1843:

"As this volume is leaving the press, intelligence has been received of a new comet being added to our system. Its orbit has been determined by the illustrious Gauss, and its period is nearly seven

years.

"The importance of this fact cannot well be overrated; for, along with Encke's and Bielas, it must advance our knowledge of some of the mysterious points connected with the constitution of the planetary scheme. We are yet ignorant whether this body has merely not been observed till now, or whether, like Lexell's, it has been constrained into a new orbit by the action of some planets."

James South and the use of his instruments. We subjoin a copy of this drawing.

This comet appeared to have a brilliant and well-defined nucleus five seconds in diameter, and a broad luminous tail of about two degrees in length.

T

THUNDER-STORMS.

The Deficiency of our present Knowledge. Of common Thunder-Clouds.-Character and Electric Charge of Clouds.-Discharge between vicinal Clouds.-Conditions for such Discharge.-Discharge between the Clouds and the Earth.-Mutual Attraction or Repulsion of Electrized Clouds.-Characters of the upper and of the lower Surface of Clouds.-Negative Testimony respecting Thunder from an isolated Cloud.-Cases of Lightning from an isolated Cloud.-A fresh Case related by M. Duperrey. Obvious Inferences from the above Cases.- Of Volcanic Thunder Clouds. Lightning from the Ashes, Smoke, and Vapor of Volcanoes.-Theoretical Ideas of its Origin.Of the Height of Stormy Clouds.-Mode of Observation.-Ascending Flashes of Lightning.-Minor Limits of the Height of Storm-Clouds.--Inefficiency of many recorded Observations.-Table of Observations as collected by Arago.-Flash of Lightning from a Cloud upward.-Of Lightning-Varieties of Lightning.-Zigzag Lightning.-Forked Lightning.-Deficiency in our Vocabulary of Terms.-Sheet Lightning-Table of Instances of Ball-Lightning.-Mr. Harris's Explanation of Ball-Lightning.-On the Speed of Lightning.-Theory of Vision illustrated by a rotating Disk.-Wheatstone's Experiments.-Observations of the Velocity of Lightning.Silent Lightning-Heat Lightning. Thunder Bursts.-Of Luminous Clouds.-Clouds themselves faintly Luminous.-Possession of the Quality in various Degrees.-Clouds visibly Luminous. Various Observations of luminous Clouds.-Sabine's Observations.-Of Thunder.-Rolling of Thunder.-Duration and Intensity of rolling Thunder.-Violent Thunder from Ball-Lightning.Interval between Lightning and Thunder.-A case in which they were almost simultaneous.Thunder without Lightning.-Noise attendant on Earthquakes.-Ŏf the Attempts to explain the Phenomena of Thunder and Lightning-Identity of Lightning and Electricity.-Whether ponderable Matter, or a Propagation of Undulations.-Difficulties of the Undulatory Hypothesis.Ball-Lightning and the Inferences to which it leads.-Bituminous Matter accompanying a Caso of Lightning Discharge.-Explanations of silent Lightnings.-Observations of silent LightningsDifficulties in the Explanation of silent Lightnings.-Arago's Suggestion for Observations.-Lightning hidden by dense Clouds.-Place of the Sound of Thunder.-Greatest Distance at which Thunder is heard.-Case of Distance beyond which it was Inaudible.-Distance at which other Sounds have been heard.-Effects of Heat, Cold, Wind, &c.-On the Transmission of Sound.Thunder heard when no Cloud was Visible.-Hypothesis of the Cause of Thunder from the Creation of a Vacuum.-Contractions and Dilatations of the Air assigned as the Cause.-Pouillet's Theory of Decompositions and Recompositions.-Influence of Echo in causing the Roll.-Duration of an Echo.-Duration of the Roll of Thunder at Sea.-Dr. Robison's Explanation of the Roll.-Application of the Theory to Zigzag Lightning.-Inefficiency of the Theory.-Means of obtaining a Minor Limit of the Length of a Flash.

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