where it might also be heard in its wrath; for all those wires could be made to pour their supplies into a large brass conductor, fixed and insulated on a table in the organ gallery, and fittingly inscribed with the words, Noli me tangere. Not far from this conductor was another brass ball forming the extremity of a metallic arrangement by which the electricity might be conveyed out of the building into the moist ground around. There was a contrivance too by which the current, when its strength became perilously great, or when its services were not required, might be turned off altogether, and discharged into the soil without entering the apartment. But if the magician wished to observe the play of the fiery element, it was easy to increase or diminish the distance between the two brass knobs, and thus to regulate the charge to be received by the huge battery employed. Then, if there were any electricity astir in the atmosphere, those balls would be sure to reveal the fact, and a succession of sparks and explosions, augmenting in rapidity as the commotion increased, would enable the observer to see into the storm as it were, and to listen to its doings related in its own voice.

The results were surprising. With this noble searching apparatus Mr. Crosse succeeded in obtaining an insight into the composition of a thunder-cloud such as no one else had done before him. Imagine a dense mass of vapour approaching the electrical observatory on a sultry summer's day. No sooner does its margin arrive overhead the exploring wire than the brass balls begin to announce the commencement of the fray. A spark is seen, a detonation heard, and these heralds of the tempest are followed by a series of mimic flashes and explosions somewhat slowly delivered, for they may not perhaps exceed nine or ten during the first minute of the convulsion. Then there is a pause, but after a while the apparatus gives forth another set of sparks and snappings, equal in number, equal also in force to those which have just been exhibited, but differing in this particularthat if the first consisted of negative electricity, the second will consist of the contrary description. Another pause takes place; and then the sparks begin to leap from ball to ball, but with greater vigour and rapidity than before; these are discharges of negative electricity as at the outset, and, when they have passed, a similar set of positive eruptions invariably ensues. Again the apparatus becomes silent, but it is only for a short interval: a more numerous and brilliant succession of flashes soon announces that another zone of negative vapour is sweeping aloft, to be followed after a brief respite by a corresponding zone of positive electricity. The intervals of repose now grow shorter, and at length a stream of fire is seen to pour from one conductor to the other,

His Dissection of Thunder-clouds.

339

broken only by the change from one kind of fluid to its opposite. When the centre of the cloud has reached the spot, and the exploring wires are sucking the lightnings from its heart, the effect is inconceivably fine. With the thunder roaring

around the building, the windows rattling in their frames, the rain dashing against the panes, the electric fire bounding madly from ball to ball, and bursting incessantly as if enraged at the presumptuous mortal who had dared to drag it from its native sky, his must be a stout heart who could witness such a scene without some feeling of awe or even of alarm. For there is death in every discharge, if those conductors were rashly approached, and thousands of Richmans might perish in the emptying of a single cloud. But as the excited vapours roll on, the explosions begin to slacken in number, and a series of twin eruptions, alternating with periods of repose, shows that the latter half of the clond corresponds in its electrical arrangements with the former. Finally, the languid spark and lazy snap announce that the hurly-burly is nearly done, or that the storm is travelling with the remnant of its wrath to some neighbouring locality.

Thus were thunder-clouds dissected. Mr. Crosse was the first who traced and defined the skeletons of these aërial rovers. To him they were no longer like whales, or weasels, or camels, or anything a Polonius might imagine; but they were masses, having a settled electrical structure, complex indeed, but as regular and harmonious as the belts of the rainbow. Formerly it was supposed that an excited cloud consisted of vapour similarly and equally charged throughout its mass. But now it appeared that there was an electrical nucleus impregnated with one species of fluid, round which ran zones of vapour arranged in pairs, each pair exhibiting positive and negative action in turn, and alternating with what seemed to be rings of repose. Further, it was manifest that the strength of the cloud lay in its centre, for the fury of the discharges gradually increased as it approached, and diminished as it receded. This circumstance was not at all in keeping with what was known respecting the dispersion of the fluid on insulating plates or globes made of a conducting material. There, the electricity is most abundant at the rim or superficies of the body: indeed, in a solid sphere it disposes itself as a thin shell or atmosphere on the exterior, leaving the inner parts perfectly unexcited. But here, in the cloud, the conditions appear to be reversed, and the fluid augments in power from the circumference to the centre.

How explain this unexpected fact? Mr. Crosse made it the topic of frequent consideration. None of the solutions he could devise seemed to afford him much satisfaction until one day,

whilst shaving, the puzzled philosopher cried out, Eureka! and darted into his electrical hall with the lather still ornamenting his chin. He proceeded to try some experiments-for theory was nothing with him until embalmed in facts-and speedily convinced himself that his surmises were correct.

The shaving discovery was this. A cloud is not a solid conducting mass, but a congregation of vesicles separated from each other by little intervals. The watery globules, if closely packed together, would convey the electricity from one part to another with the greatest facility, but being estranged by the action of caloric, the fluid can only be propagated to a small distance by direct communication. Induction, however, commences where transmission ceases. Hence, if we suppose electricity to be developed in any particular spot in such a medium, it will spread itself circularly as far as its energy will enable it to push through the interspaces between the surrounding vesicles. Then it will begin to act inductively through the air, calling up the opposite kind of fluid in a ring or zone of watery particles, which ring or zone will be concentric with the excited nucleus. This, in its turn, necessitates the formation of another belt charged with the contrary species of electricity, and thus the whole cloud is mapped out into a series of electrical rings, arranged in pairs, with barren intervals, and a central mass, which is the metropolis of the storm. If the distribution of the fluids could be rendered visible, and their presence denoted by different colours vying with those of the rainbow in brilliancy-the interspaces being left in their natural condition-what an impressive spectacle such a cloud would present as it rose above the horizon, mounted to the zenith, and then spread its huge folds over the heavens, like some monster serpent-say the Old Serpent of Sin let loose from his invisibility, and coming in horrible magnificence to crush the world in his embrace. In the absence, however, of these pictorial aids, some of Professor Faraday's experiments afford a species of illustration which may assist the reader's conception of the case. If a number of small pails or vessels are arranged within each other-all being insulated by the interposition of sheets of shell-lac or some other nonconducting substance-and if a ball charged with electricity be suspended within the innermost vessel, its inductive effects upon the whole set will express in some degree the action of the storm-nucleus upon the remainder of the vaporous mass.

Nor is the interest of such a many-zoned cloud at all lessened by the fact that it produces a corresponding disturbance and a

It is scarcely necessary to remark that in speaking of this adjustment into zones, it is not the vapour, but the electricity that is meant.

Fiery Character of a November Fog.

341

corresponding distribution of the electricity in the earth beneath. Point for point, ring for ring, and nucleus for nucleus, it calls up an answering tide of fluid in the ground by virtue of its inductive powers, the only difference being that the positive parts of the vapour above are represented by negative below, and vice versa. Thus, whilst a storm is raging, we are helplessly stationed between two excited masses, and if we were relatively as light as the paper figures or pith balls which frolicsome young electricians delight to see dancing between two metallic plates, we might almost expect to be turned into moveable conductors, and kept mounting and descending until the troubled equilibrium was restored. Thus, too, whilst the storm-cloud courses through the atmosphere, its electrical rival is travelling along the surface with equal rapidity, as if it were but the shadow of the tempest above; and now and then the vivid flashes, darting from one nucleus to the other, or from one zone in the sky to another in the earth, seem like the shots which armies moving by parallel paths sometimes exchange in their wrath or in their wanton

ness.

It does not, however, require a professed thunder-storm to produce stupendous electrical displays. Mr. Crosse's apparatus enabled him to read the secrets of a November mist, and those who have frequently pushed their way through these cold, raw, dreary phenomena will be surprised to learn how often they may have been sheeted in fire, and how calmly they have passed through a furnace more deadly than Nebuchadnezzar's, but without a hair of their heads being singed in the flames. One day, during that dismal month which Hood celebrates in a series of No-es, the philosopher was seated in his hall of thunderbolts whilst a thick driving fog was darkening the air. For some time no symptoms of excitement were manifested by the exploring machine: the insulators were dripping with wet, and consequently carried off all the electricity the wires received. suddenly a smart detonation was heard between the two balls; others shortly followed, and then the explosions succeeded each other so swiftly that the ear could detect nothing but a continuous crash. This was interrupted by the transition to the opposite kind of electricity, after which a similar torrent of fluid was poured from one conductor to the other. So vivid was the rush of fire that the eye could not bear to survey it for any length of time. To have touched one of those balls whilst the liquid lightning was gushing forth with such fury would have been instant death. For upwards of five hours this splendid but appalling spectacle continued without any intermission except when the positive fluid was exchanged for the negative.

But

Had

'it not been for my exploring wire,' says Mr. Crosse, I should not have had the slightest idea of such an electrical accumula'tion in the atmosphere. . . . the stream of fluid far exceeded anything I ever witnessed, except during a thunder-storm. Had the insulators been dry, what would have been the effect? In every acre of fog there was enough of accumulated electricity to have destroyed every animal within that acre.' Who could have supposed that a simple mist contained such potent lightnings ready to be issued whenever the word of command was given, and yet so masked and sheathed that but for the tell-tale apparatus you would as soon have imagined the gentle dews to be saturated with fire? This, however, is no solitary exemplification of the skill with which the Great Forces of Nature are curbed and muffled when their activities would be injurious to man. The sea consists of two gases, which, if released from their combination, would produce the intensest flame and burn up every combustible thing on the surface of the globe. The atmosphere is formed of elements which might easily be transformed into compounds capable of poisoning, maddening, or suffocating every creature that breathes. The clouds, which now discharge their contents in such harmless drops, might pour out their burdens in a deluge as if some huge reservoir had burst in the sky, and crush every object that lay beneath. The winds might sometimes be expected to break loose, and, forgetting their prescribed pace, would gallop round the globe, tearing up our towns by the roots and driving men and trees before them like dust in a gale. The ties of chemical affinity might relax, or the cohesive forces might occasionally fail, and then the earth would crumble into a heap of sand. The internal fires of the earth might master the resistance of the external shell, and shatter the surface at a stroke; or, collapsing in their fury, the ceiling of the gulf might give way and whole kingdoms go down into the burning abyss. Half an hour's slumber on the part of the Almighty would liberate all these great powers from their present restraints, and in that half hour the world would be reduced to a wreck. But He who holds the winds in His fists, hides His thunderbolts in the drifting vapour and chills the very lightnings so that men walk unscathed through the deadliest magazine of mist.

The electrical battery, through whose agency Mr. Crosse was enabled to observe these striking phenomena, consisted of fifty jars with a coated surface of seventy-three square feet. Though it required upwards of two hundred turns of the wheel of a machine with a twenty-inch cylinder to charge it artificially, those