271. Numerous cases of the successful application of electricity as a medical agent have been published by different authors; Mr. Cavallo has related some of a very striking nature, as have also Mr. Carpue, and Mr. Ferguson, whose testimony stands high in consequence of the candor and unaffected simplicity of their narrations. To the above-mentioned names we must add the name of Mr. La Beaume, who has recently published an excellent little work on the Application of Galvanic Electricity in the cure of chronic diseases; to these works the reader is referred for more ample information on the subject than our limits will allow us to give. PART IV. ATMOSPHERICAL ELECTRICITY. 272. In the preceding parts of this article we have had occasion to make several references to the identity of lightning and the electricity excited by artificial means; we now proceed to show, by a selection of strictly appropriate experiments, that that agent which is ever active in the atmosphere which surrounds our earth, and is occasionally producing some of the most astonishing, and awfully grand phenomena of nature, is nothing more than a vast explosion of accumulated electricity. 273. The discovery of this important fact was by no means an instantaneous thing; even some modern writers on philosophy appear to have formed opinions on the nature of lightning essentially incorrect; and this is the more remarkable when it is considered that, so long ago as the days of the abbé Nollet, such remarks as the following should have been published, and read, and verified by actual experiment soon after. ‘If,' said the abbé, any should take upon him to prove, from a well-connected comparison of phenomena, that thunder is in the hands of nature what electricity is in ours; that the wonders we now exhibit at pleasure are little imitations of those great effects which frighten us; and that the whole depends on the same mechanism: -if it could be shown, that a cloud prepared by the action of the winds, by heat, by a mixture of exhalations, &c. is, when opposite to a terrestrial object, that which an electrified body is, when at a certain distance from one that is not electrified; I confess this idea, if it were well supported, would afford me much pleasure; and to support it, how many specious reasons present themselves to a man well versed in electricity. The universality of the electric matter, the rapidity of its action, its inflammability, and its activity in inflaming other bodies; its property of striking bodies externally and internally, even to their smallest parts, the remarkable example we have of this effect in the Leyden experiment, the idea we may legitimately form in supposing a greater degree of electric power, &c. All these points of analogy, which I have for some time meditated, begin to make me believe that one might, by taking electricity for a model, form to one's-self, in relation to thunder and lightning, more perfect and probable ideas than any that have been hitherto offered.' 274. This was certainly a bold nypothesis; highly creditable to the judgment of the author, and affording no obscure intimation that elec tricity was about to make some unprecedented degree of progress; but to Dr. Franklin undoubtedly belongs the honor of accomplishing, by actual experiment, all that the abbé Nollet's penetrating sagacity led him to speak of in the words just quoted. In a series of letters to one of the members of the Royal Society, the Dr. first gave in detail an hypothesis to explain the phenomena of thunder and lightning by the known properties of electricity, which was soon followed by a demonstration of its truth in the most remarkable experiment ever made. The 275. The following are the leading points of resemblance which Dr. Franklin observed to obtain between the electricity of the atmosphere and that which is produced by artificial means. (1.) The zig-zag appearance of the lightning is exactly the same as that of a strong electric spark when it passes through a considerable interval of air. (2.) Lightning generally strikes such bodies as are high and prominent, as the summits of high hills, the tops of lofty trees, high towers, spires, masts of ships, points of spears, &c., and the electric fluid always passes through the most prominent parts, when striking from one body to another. (3.) Lightning is observed to strike most frequently into those substances that are good conductors of electricity, such as metals, water, and moist substances; and to avoid those that are non-conductors. (4.) Lightning inflames combustible bodies. same is effected by electricity. (5.) Metals are melted by a powerful charge of electricity. This phenomenon is one of the most common effects of a stroke of lightning. (6.) The same may be observed of the fracture of brittle bodies, and of other expansive effects common to both causes. (7.) Lightning has been known to strike people blind. Dr. Franklin found, that the same effect is produced on animals when they are subjected to a strong electric charge. (8.) Lightning destroys animal life. Dr. Franklin killed turkeys of about ten pounds weight, by a powerful electric charge. (9.) The magnetic needle is affected in the same manner by lightning and by electricity, and iron may be rendered magnetic by both causes. The phenomena are, therefore, strictly analogous, and differ only in degree; and, if an electrified gun-barrel will give a spark, and produce a loud report at two inches distance, what effect may not be expected from perhaps 10,000 acres of electrified cloud? And is not the different extent of these conductors, equal to the different limit of their effects? 276. Reasoning on these strong resemblances, Franklin formed the design of erecting a conducting rod by which the lightning might be drawn from the clouds, and thus afford an opportunity of ascertaining its identity with the electric fluid. The electric fluid,' said he, 'is attracted by points; we do not know whether this property be in lightning; but since they agree in all the particulars in which we can already compare them, it is not improbable that in this they likewise agree. Let the experiment be made.' doubtless he would himself have made it before And any other person could have anticipated him in it, but waiting for the erection of a spire in Philadelphia, and his opinions becoming known, he was anticipated by the French philosophers D'Alibard and De Loe, who erected a rod such as Franklin had suggested, and succeeded in the experiment. But the honor and merit of the idea were not to be thus rent from Franklin; for in the mean time, and without any knowledge of the attempts of the French electricians, it occurred to him that, by sending up a kite, he could obtain a readier access to the clouds than by the longest rod which he could raise on the highest spire. He made the attempt, and, as we have before shown, was successful; and thus was the identity of lightning with electricity satisfactorily established. 277. In treating of the electricity of the atmosphere it may be proper to begin with the more gentle and silent manifestations of it: thence to proceed to the consideration of its accumulated discharges in meteors and thunder-storms; and then make some remarks on its general influence on the surface of our earth. 278. From long, correct, and patient investigation, it has been proved that the various luminous phenomena that appear in our atmosphere, are to be resolved into the agency of electricity, although it must be allowed that, with all our knowledge of those effects, they are still surrounded with such difficulties, that scientific men are not quite of one mind respecting them. Of this description the aurora borealis, or northern light, must be allowed to be an instance. 279. The aurora borealis, or, as the same appearance is commonly termed, streamers, and in the Shetland Isles, the merry dancers, can seldom be seen in the southern parts of the kingdom; and, even when seen there, the appearance is far less brilliant than in northern latitudes, where this wonderful phenomenon is the constant attendant of clear evenings, affording a great relief to the inhabitants, amid the gloom that would otherwise attend their dreary winter nights. 280. Of this kind of meteor, the late Mr. George Adams has given the following concise account in his valuable lectures :-The appearances of the aurora come under four different descriptions. (1.) A horizontal light, like the morning aurora, or break of day. (2.) Fine, slender, luminous beams, well defined, and of dense light. These often continue a quarter, a half, or a whole minute, apparently at rest, but oftener with a quick lateral motion. (3.) Flashes pointing upward, or in the same direction with the beams, which they always succeed. These are only momentary, and have no lateral motion; but they are generally repeated many times in a minute. They appear much broader, more diffuse, and of a weaker light than the beams: they grow gradually fainter till they disappear; and sometimes continue for hours, flashing at intervals. (4.) Arches, nearly in the form of a rainbow: these, when complete, go quite across the heavens, from one point of the horizon to the opposite point. 281. When an aurora happens, these appearances seem to succeed each other in the follow ing order :-(1.) The faint rainbow-like arches ; (2.) The beams; and (3.) The flashes. As for the northern horizontal light, it appears to consist of an abundance of flashes of beams, blended together by the situation of the observer. The beams of the aurora borealis appear at all places to be arches of great circles of the sphere, with the eye in the centre; and these arches, if prolonged upwards, would all meet at one point. The rainbow-like arches all cross the magnetic meridian at right angles. When two or more appear at once they are concentric, and tend to the east and west; also the broad arch of the horizontal light tends to the magnetic east and west, and is bisected by the magnetic meridian; and when the aurora extends over any part of the hemisphere, whether great or small, the line separating the illuminated part of the hemisphere from the clear part is half the circumference of a great circle crossing the magnetic meridian at right angles, and terminating in the east and west: moreover, the beams perpendicular to the horizon are only those on the magnetic meridian. That point in the heavens to which the beams of the aurora appear to converge, at any place, is the same as that to which the south pole of the dipping-needle points at that place. The beams appear to rise above each other in succession; so that, of any two beams, that which has the higher base has also the higher summit. Every beam appears broadest at or near the base, and to grow narrower as it ascends; so that the continuation of the bounding lines would meet in the common centre to which the beam tends. 281*. Now between these appearances and those of electricity, under certain circumstances, there are several points of close resemblance. For it is found by a simple experiment that, when the electric fluid is made to pass through rarefied air, it exhibits a diffused luminous stream, which has all the characteristic appearances of the northern lights. There are to be seen the same varieties of color and intensity, the same undulating motion and occasional corruscations; the streams exhibit the same diversity of character, at one moment minutely divided into ramifications, and at another beaming forth in one body of light, or passing in well defined flashes; and, when the rarefaction is high, various parts of the stream assume that peculiar glowing color which occasionally appears, and which, on the whole, leaves but little room to doubt that the phenomena are produced by the passage of electricity through the upper regions of the atmosphere, although at the same time it ought to be mentioned that this opinion has been doubted by some since the accomplishment of the recent voyages of discovery to the polar regions. 282. It has been stated above, that this most beautiful phenomenon is seldom witnessed by the inhabitants of the southern parts of the kingdom; to them, therefore, at all events, as well as to those who have witnessed the aurora borealis in a fainter degree, the following extract from Mr. Dalton's description of one which he witnessed must be acceptable. It is taken from his Meteorological Essays. 283. Attention,' says Mr. Dalton, 'was.first excited by a remarkably red appearance of the clouds to the south, which afforded sufficient light to read by, at eight o'clock in the evening, though there was no moon, nor light in the north. Some remarkable appearance being expected, a theodolite was placed to observe its altitude, bearing, &c. From half past nine to ten o'clock, P. M., there was a large, luminous, horizontal arch to the southward, almost exactly like those which we see in the north; and there were some faint concentric arches northward. It was particularly noticed that all the arches seemed exactly bisected by the plane of the magnetic meridian. At half past ten o'clock streamers appeared very low in the south-east, running to and fro from west to east; they increased in number, and began to approach the zenith apparently with an accelerated velocity; when all on a sudden the whole hemisphere was covered with them, and exhibited such an appearance as surpasses all description. The intensity of the light, the prodigious number and volatility of the beams, the grand intermixture of all the prismatic colors in their utmost splendor, variegating the glowing canopy with the most luxuriant and enchanting scenery, afforded an awful, but at the same time the most pleasing and sublime spectacle. Every one gazed with astonishment; but the uncommon grandeur of the scene only lasted about one minute; the variety of colors disappeared, and the beams lost their lateral motion, and were converted into the usual flashing radiations; but even then it surpassed all other appearances of the aurora, in that the whole hemisphere was covered with it. 284. Notwithstanding the suddenness of the effulgence at the breaking out of the aurora, there was a remarkable regularity in the manner. Apparently a ball of fire ran along from east to west, and the contrary, with a velocity so great as to be barely distinguishable from one continued train, which kindled up the several rows of beams one after another: these rows were situated before each other with the most exact order, so that the bases of each row formed a circle crossing the magnetic meridian at right angles; and the several circles rose one above another in such sort, that those near the zenith appeared more distant from each other than those near the horizon, a certain indication that the real distances of the rows were either nearly or exactly the same. And it was further observable that, during the rapid lateral motion of the beams, their direction in every two nearest rows was alternate; so that whilst the motion in one row was from east to west, that in the next was from west to east. 285. The point to which all the beams and flashes of light uniformly tended was, in the magnetic meridian, and, as near as could be determined, between 15° and 20° south of the zenith. The aurora continued, though diminishing in splendor, for several hours. There were several meteors seen at the same time; they appeared below the aurora, and unconnected with it.' This brilliant display of the aurora borealis Mr. Dalton witnessed on the 13th of October, 1792. 286. Similar appearances are often seen towards the south pole, but they are said to be unattended with the same variety of color; they are called aurora australis. A very feeble, though certainly a pleasing imitation of this remarkable phenomenon may be thus exhibited :-Take the glass vessel represented in fig. 9, resembling a Florence flask, and fitted with a valve at top by which it may be exhausted of its air: when exhausted, and rubbed in the common manner used to excite electrics, it will appear luminous within, being full of a flashing light which plainly resembles the aurora borealis, or northern light. This phial may also be made luminous, by holding it by either end, and bringing the other end to the prime conductor; in this case all the cavity of the glass will instantly appear full of flashing light, which remains in it for a considerable time after it has been removed from the conductor: instead of the glass phial a glass tube exhausted of air and hermetically sealed may be used, and perhaps with more advantage. The most remarkable circumstance of this experiment is, that if the phial or tube, after it has been removed from the conductor (and even several hours after its flashing light has ceased to appear), be grasped with the hand, strong flashes of light will immediately appear within the glass, which often reach from one end to the other. 287. The next form of atmospherical electricity that claims our attention is that which it assumes in those meteors, to which the vulgar name of falling, or shooting stars, has been given. The aurora borealis, we have said, is caused by streams of the electric fluid passing rapidly through the higher regions of the air; and these phenomena of which we are now speaking, are, in all probability, portions of the same matter moving through a more resisting medium, since they are always observed to be in comparatively small altitudes. 288. These meteors vary considerably in their size and color, and also in the rapidity of their motion; they move in various directions, but chiefly incline towards the earth. They occur in different states of the atmosphere, but prevail most in clear frosty nights, and at other times when the winds are easterly, and the sky clear; in the intervals also of showery weather they are frequent, and on summer evenings, when well defined clouds are seen floating in a clear atmosphere. 289. In favorable states of the atmosphere, Mr. Singer remarks, these appearances are seen to succeed each other so rapidly, that he has often counted thirty of them in the space of an hour, and, on some occasions, twice that number. The frequency of their occurrence, he thinks, indicates that they are produced by some of the usual atmospherical changes, and that the circumstance of their explosion being unattended by the fall of stones, renders it almost certain that their nature is essentially different from that of the large meteors. 290. The same gentleman offers the following as arguments in favor of the electrical origin of these meteors:(1.) The light of falling stars is similar to the light of the electric spark. (2.) They occur as frequently and as irregularly as other electrical changes in the atmosphere. (3.) Their motion, like that of electricity, is exceedingly rapid; and the longest interval through which they strike, is traversed in an interval of time too minute to admit of measurement. (4.) They occur most frequently during, or near to those changes of weather, that are known to influence the electrical state of the atmosphere. (5.) Their direction is never constant; they occur in every part of the atmosphere, and move in almost every direction; such is also the case with lightning. (6.) The appearance of falling stars may be accurately imitated by electricity; and the circumstances on which the success of such experiments depend, are such as are likely to occur in the production of the natural phe nomena. 291. Hence if electricity be passed gradually through an exhausted receiver, it assumes, as we have already seen, the appearance of the aurora borealis; but if an accumulation of it be suddenly transmitted, it will pass through the receiver with the straightness and brilliance of a shooting star. This appearance also occurs most readily when the receiver is but partially exhausted. The imitation therefore of these two phenomena seems evidently to require the same conditions for its production, as those which obtain in nature; that is to say, the aurora occurs in those regions where the air is highly rarefied; and the most complete imitation of it is effected in a thoroughly exhausted receiver; falling stars take place where the air is much more dense, and the imitation of them requires a medium which offers from its density considerable resistance. 292. Different writers on electricity have proposed different methods of producing an imitation of these meteors, but that of Mr. Singer is undoubtedly the most effectual as well as the most elegant. He used for this purpose a glass tube, five feet in length, and about five-eighths of an inch in diameter, mounted with a brass cap at each end, and fitted at one extremity with a valve to allow of its being exhausted. When this tube was exhausted, no spark would pass through it except in a very diffused state; but when the charge of a very large jar was employed, a brilliant spark was obtained through the whole length of the tube, resembling in appearance a shooting star. 293. There are various other luminous appearances of the electricity of the atmosphere, which might with propriety be described here, such as those frequently observed on the tops of spires, and the masts of ships, and occasionally on the points of spears, &c.; but we must not enlarge, and shall only observe respecting them, that they seem analogous to the light tha is observed on the point of any slender and prominent conductor, when placed within an electrical atmosphere, or brought Lear to an excited electric. These, and similar phenomena observable in the atmosphere, will be fully treated of in the article METEOROLOGY. 294. But the most magnificent display of atmospnerica electricity is to be seen during a thunder-storm, the particular phenomena of which we must now proceed to notice. We have already seen the most satisfactory ground for the conclusion that lightning and electricity are identical, and have adverted to most of the known means by which the latter are produced: and if the analogy be correct in the one case we may conclude it to be so in the other, although with some differences perhaps, which have hitherto been, and which may for ever remain inaccessible to human observation. 295. If then, it be asked, whence comes the electricity of the atmosphere? it may in reply be said, that from the sum of our knowledge respecting meteorological phenomena, there appears good reason to conclude that the causes which produce artificial electricity, are all in full operation in the masses of vapor, among which natural electricity appears active. 296. This opinion is maintained by several eminent practical electricians of the present day; it was warmly espoused by the late Mr. Singer, who advanced in support of it the following positions:-(1.) That the electrical phenomena of the atmosphere take place, in all climates, to the greatest extent, about the period of the greatest degree of heat, when the rays of the sun have caused a considerable accumulation of vapor. (2.) Where this cause operates to the greatest extent, as, for instance, within the tropics, natural electricity is produced on the largest scale. (3.) When the natural source of evaporation is assisted by collateral causes, electrical changes occur with astonishing activity, as in the eruption of a volcano, or the heat imparted to the air in its passage over large extents of hot sands, as those of Africa. (4.) By the action of winds, currents of air of different temperatures are often mixed, so that such as have been heated and charged with moisture, become suddenly cooled, thus occasioning a precipitation of water, and the occurrence of electrical changes. This is often witnessed on the coast of Guinea during the existence of the harmattan. (5.) These electrical changes are every where most frequent when the causes of evaporation and condensation suddenly succeed each other. 297. After advancing several cogent arguments in favor of the above facts, and noticing in a very candid manner some objections urged against the theory they are intended to support, Mr. Singer concludes with the following truly appropriate and judicious observations :- Although the immediate causes by which the various phenomena of the atmosphere are produced, be still far beyond our comprehension; yet the connexion of their several effects is a sufficient demonstration that they are not purely mechanical, but subservient to the direction of supreme power and intelligence. By this means the most simple arrangement becomes the source of sublime effects. The process of evaporation which modifies the action of the sun's rays, and conveys to every part of the earth's surface a source of fertility, does at the same time diversify the appearance of the atmosphere by an endless variety of imagery, enlivening the horizon with the most brilliant and glowing tints and in all probability effecting those electrical changes, which are the precursors of the most magnificent phenomena in nature.' 298. The phenomenon of the thunder-storm itself is always one of intense interest to the electrician. Some writers on the subject of electricity have furnished us with very beautiful descriptions of a thunder-storm, but of all these we feel disposed to give the preference to that of Sig. Beccaria, as containing a neat and unvarnished statement of facts, instead of being decorated with the effusions of a poetical imagi nation. 299. Thunder-storms,' says Beccaria, generally happen when there is little or no wind; and their first appearance is marked by one dense cloud, or more, increasing very fast in size, and rising into the higher regions of the air; the lower surface black, and nearly level, but the upper finely arched, and well defined. Mary of these clouds seem frequently piled one upon another, all arched in the same manner; but they keep continually uniting, swelling, and extending their arches. 300. At the time of the rising of this cloud, the atmosphere is generally full of a great number of separate clouds, motionless, and of odd and whimsical shapes. All these, upon the appearance of the thunder-cloud, begin to move towards it, and become more uniform in their shapes as they approach, till, coming very near the thunder cloud, they mutually stretch towards one another, immediately coalesce, and together make one uniform mass. But sometimes the thunder-cloud will swell, and increase very fast, without the conjunction of these adscititious clouds, the vapors of the atmosphere forming themselves into clouds wherever it passes. Some of the adscititious clouds appear like white fringes at the skirts of the thunder-cloud, but these are continually growing darker and darker as they approach or unite with it. 301.When the thunder-cloud is grown to a great size, its lower surface is often ragged, particular parts being detached towards the earth, but still connected with the rest. Sometimes the lower surface swells into various large protuberances, bending uniformly towards the earth. When the eye is under the thunder-cloud, after it is grown larger, and well formed, it is seen to sink lower, and to darker. prodigiously; at the same time that a number of adscititious clouds (the origin of which can never be perceived) are seen in a rapid motion, driving about in every direction under it. While these clouds are agitated with the most rapid motions, the rain generally falls in the greatest plenty; and, if the agitation is exceedingly great, it commonly hails. 302. 'While the thunder-cloud is swelling, and extending its branches over a large tract of country, the lightning is seen to dart from one part of it to another, and often to illuminate its whole mass. When the cloud has acquired a sufficient extent, the lightning strikes, between the cloud and the earth, in two opposite places, the path of the lightning lying through the whole body of the cloud and its branches. The longer this lightning continues the rarer the cloud grows, and the less dark is its appearance, till at length it breaks in different places, and displays a clear sky.' 303. From the circumstance of almost constant injury attending thunder-storms it is impossible to witness one without some feelings of personal danger; in this case attention to the following observations may often be of service in relieving the mind from unnecessary fear, or in suggesting the necessary steps to be taken for the prevention of accident. 304. The Place of the Explosion.-The electrical explosion generally takes place in the air, and at a considerable height; but in many instances it happens between the clouds and the earth. In most instances, perhaps, the lightning descends from the clouds to the earth, and the explosion is then called the descending stroke: but in some cases it is known to pass from the earth to the clouds, and is then termed the ascending stroke: of the latter kind appears to have been the explosion which took place on the Malvern hills, in the summer of 1826, and which was attended with such melancholy consequences. A very curious instance of the ascending stroke is related by G. F. Richter, in his work on thunder. He informs us that in the cellar belonging to the Benedictine monks of Fontigno, while the servants were employed in pouring into a cask some wine which had been just boiled: a fine light flame appeared round the funnel, and they had scarcely finished their operation when a noise like thunder was heard; the cellar was instantly filled with fire; the cask was burst open, although hooped with iron, the staves were thrown with prodigious violence against the wall; and, on examination, a hole of three inches diameter was found in the bottom of the cask. 305. The Distance of the Thunder Cloud.-This is a point of some importance to be determined; and the interval between the flash and the commencement of the report furnishes the data necessary for the calculation. Sound travels at the rate of 1142 feet in a second: consequently, by a watch which beats and points the seconds, the distance of the cloud is easily ascertained, for the flash and the sound are really contemporaneous ; and the former requires hardly any perceptible lapse of time to travel through any ordinary distance. Thus, for example, suppose the flash to occur five seconds before the sound is heard, then 1142 × 557101 mile 430 feet, the distance of the explosion from the place of the observer. So far this calculation is very gratifying, but it is no criterion of safety, for it only indicates the distance of a discharge that has taken place: the next may render the observer incapa ble of observation. 306. Indications of real danger.-During a thunder-storm there are certain circumstances which afford strong indications of actual danger. Such, for instance, are a rapid approach of the charged cloud, and the almost perpendicular direction of the lightning. When the cloud seems to be vertical as soon as it is formed, we are exposed to its utmost fury; and, when it increases In darkness as it approaches, it also indicates great danger. When the flashes strike perpen |