1854.] 



ATMOSPHERICAL ELECTRICITY. 



155 



the state of civilization in Ethiopia, and after we had taken the 

 most exact plans of the localities, we proceeded in six days, by 

 the desert Gilif to Gebel Barkal, where we arrived on the 6th 

 of May. Here was the more northern, the more ancient, and, 

 to judge by the remains, also the more important capital of the 

 state of Meroe. At the foot of this single mass of rock, which 

 rises in an imposing manner, and is called there, in the hierogly- 

 phical inscriptions, "The Sacred Mountain," is situated Napata. 

 The history of this place, which we may still derive from its ruius, 

 gives us at once a key to the relations which subsisted in 

 general between Ethiopia and Egypt, as regards the history of 

 their civilization. We find that the most ancient epoch of art in 

 Ethiopia was purely Egyptian. It is as early as the period of 

 the great Ramses, who, of all the Pharaohs, extended his power 

 farthest, not only towards the north, but also towards the south, 

 and testified this by monuments. At an early period he built a 

 great temple here. The second epoch begins with King 

 Tahraka, also known as the ruler of Egypt, the Thirhaka of the 

 Bible. This spot was adorned with several magnificent monu- 

 ments by him and his immediate successors, and though they 

 were built in a style now employed by native kings, it is, never- 

 theless, only a faithful copy of the Egyptian style. Lastly, the 

 third epoch is that of the kings of Meroe, whose dominion 

 extended as far as Pkike, and was manifested also at Gebel 

 Barkal by numerous monuments. On an intermediate journey 

 into the Cataract country, situated farther up the river, which 

 we had cut off by the desert journey, I found only middle-age, 

 but no ancient Ethiopian remains of buildings. 



(To be continued.) 



Atmospherical Electricity* 



BY PROFESSOR JOSErH LOYERIXG, OP HARVARD UNIVERSITY. 



If we allow ourselves to be instructed by the analogies of the 

 friction electrical machine, the Leyden jar, or the voltaic battery, 

 we shall find that the essential condition for maintaining a charge 

 of electricity, is the existence of two bodies or portions of the 

 same body (which are generally conductors) separated from each 

 other bv a non-conducting medium. An electrical charge im- 

 pties the presence of two bodies in opposite electrical states ; and 

 the well-known attraction mutually exerted by two such bodies 

 would lead soon to a discharge, if they were not separated by 

 the insulating medium. There is no reason why the solid earth 

 should not play the part of one of these bodies, while the other 

 is represented by the upper regions of the atmosphere or by the 

 clouds floating therein. As the surface of the solid earth is 

 separated from the region of clouds by the non-conducting air, 

 an electrical charge may be maintained by the earth on the one 

 hand, and by the clouds on the other, and this charge will be 

 limited in intensity only by the dryness of the intervening air. 

 Thus the whole earth resembles a Leyden jar, or more exactly, 

 on account of the large distance between the clouds and the 

 earth, an electrical machine, in which the rubber is moved from 

 the prime conductor by a larger space than that which separates 

 the two coatings of the jar, and in which, therefore, the electricity 

 is more free than in the jar. 



Observation shows that this electrical charge which the planet 

 is capable of sustaining, it generally does sustain to a greater or 

 less degree. As every change in the condition of matter, 

 whether mechanical, physical, or chemical, places it in the elec- 

 trical state — as heat, both directly and by leading to combustion 

 and evaporation, provokes this electrical state. — We are at no loss 



for excitino- agents which shall give to the earth and clouds the 

 whole or a part of the electricity which they are designed to 

 hold. 



I shall consider, — 1. The ways in which the electrical state of 

 the atmosphere is investigated. 2. The results to which this 

 investigation conducts. 3. The probable causes of atmospherical 

 electricity. And 4. The effects, or the phenomena occurring in 

 meteorology or elsewhere which originate in electrical action. 



One way in which the electrical state of the air is examined 

 is by erecting a metallic rod, insulating it from its supports, 

 pointing it at the top, and connecting the lower end with an 

 electrometer. It was on such a rod, erected at Marly-la-Ville 

 according to the directions of Franklin, that Coiffier, the servant 

 of Dalibard, first obtained by a premeditated experiment sparks 

 of atmospherical electricity such as were anticipated from 

 Franklin's prediction. Sometimes the apparatus well known 

 under the name of " the electrical chime of bells'' is attached to 

 rods, which have been elevated either for the purpose of study- 

 ing or of guiding atmospherical electricity, and, by the peal 

 which it sends forth when the electricity descends, this secret of 

 nature is betrayed to all within hearing of the sound, and the 

 attention of the observer is called to his duty. Murray speaks 

 of seeing a set of these electrical bells attached to a lightning- 

 rod near a gateway in Zug, the capital of the Canton, and 

 another in a garden on the route from Zurich to Basle. 



When it is desired to make experiments upon greater heights 

 than can be reached by rods, Saussure proposed to throw a ball 

 into the air by means of an arrow or otherwise. A fine wire 

 was attached by one end to this ball, and was carried up with it 

 The other end was connected with an electrometer. A long 

 wire suspended from a balloon may be used for the same pur- 

 pose, as was done by Gay-Lussac and Biot, in their celebrated 

 scientific excursions into the air. Becquerel and Breschet em- 

 ployed Saussure's method in their experiments made on the 

 top of the Great St. Bernard. Having spread out upon the 

 ground a piece of gummed sarcenet about eight feet square, 

 upon which they enrolled two hundred and fifty feet of silk 

 cord interlaced with fine wire, they sent it up on the tail of an 

 arrow. The motion of the arrow through the air would not 

 produce of itself any electricity, unless the air were moist. To 

 be certain, however,. that no electricity produced by the mode of 

 making the experiment should come in to vitiate the results, 

 these observers first sent the arrow in a horizontal direction, 

 without being able to effect the electroscope. 



Another method, at first so striking but now so trite, of making 

 experiments upon atmospherical electricity, is by flying the kite. 

 Here, indeed, was philosophy in sport made science in earnest. 

 Franklin first made this bold experiment, of enticing down the 

 lightning upon the kite-string, familiar to the world on the 15th 

 of June, 1752. Science, poetry, patriotism, will repeat the thread- 

 bare story of the strips of cedar united into a cross and covered 

 with a silk handkerchief, of the key, of the silk ribbon by which 

 he held the string, of his early anxiety and his first disappoint- 

 ment while the string was dry, and his final exultation when the 

 rain wetted it, the hempen fibres began to fly apart, and he drew 

 the first spark of lightning on his knuckles. Romas, for whom 

 Martins has unaccountably claimed priority in the kite experi- 

 ment attempted to repeat it on the 14th of May, 1753. The 

 weather seemed propitious for the object, but he could get no 

 spark. On the 17th of June he raised a kite with 780 feet of 

 string 550 feet high in the air, and having taken the precaution 

 to twist a fine wire into his kite string he succeeded in obtaining 

 sparks three inches long and one quarter of an inch in thickness. 



