304 



ELECTRICAL EXHIBITION AT PHILADELPHIA. 



of all arms. On the 10th of January Col. Bur- 

 naby left Korti with a supply of corn for Stew- 

 art's detachment. Another column was sent 

 up the river to Abou Hamed, for the purpose 

 of opening the route across the Nubian Desert 

 from Korosko, or the Berber route from Sua- 

 kin, for the transport of supplies and re-enforce- 

 inents. Gen. Wolseley's force at Korti when 

 he divided it into three detachments was prob- 

 ably not over 5,000 men, as half of his army 

 was still struggling against the eddies of the 

 middle cataracts. On the 20th of January, 1885, 

 came the disheartening intelligence that Gen. 

 Stewart's column had sustained an attack of 

 the enemy in greatly superior numbers at Abu 

 Klea Wells, losing, out of about 1,500 men, 4 

 field officers, 5 line officers, and 65 rank and 

 file killed, and 9 officers and 85 rank and file 

 wounded. Among the killed was the dashing 

 and experienced Col. Burnaby. Sir Herbert 

 Stewart was wounded. The column stood its 

 ground, formed in a single square, which was 

 assailed on all sides, and finally repelled the 

 Arabs. A day or two later the intelligence 

 came that Gen. Stewart had continued his ad- 

 vance and took up a position at Gubat, near 

 Metemneh, opposite Shendy. He was sup- 

 ported here by a detachment sent by Gen. 

 Gordon in his steamers. Col. Sir Charles 

 Wilson embarked in a steamer for Khartoum. 

 When he arrived there he was fired upon from 

 the works, and soon convinced himself that the 

 city had been taken by the Mahdi. On his re- 

 turn his steamer was wrecked below the Shnb- 

 laka Cataract, and the party stranded on an 

 island. From native accounts it appeared 

 probable that the Mahdi introduced emissaries 

 into the town who worked upon the religious 

 feelings of the soldiers, that the enemy were 

 admitted by one Faraz Pasha, the .officer of the 

 day, that 7,500 of the garrison deserted to the 

 enemy, leaving 2,500 faithful to Gen. Gordon, 

 and that these fought desperately until over- 

 whelmed. Most accounts agreed that Gen. 

 Gordon was killed. 

 EGYPT, EXPLORATIONS IN. (See AECH^OL- 



OGY.) 



ELECTRICAL EXHIBITION AT PHILADELPHIA. 



This exhibition, which was opened Sept. 2, 

 1884, under the auspices of the Franklin In- 

 stitute in Philadelphia, illustrates the advance- 

 ment of electrical science and its growing im- 

 portance in the mind of the scientist, as well 

 as its practical applications in domestic econo- 

 my. Where these great buildings stand to-day, 

 Benjamin Franklin, one hundred and thirty 

 years ago, sailed his famous kite, and from the 

 clouds drew the spark that kindled the New 

 and the Old World with enthusiasm. After 

 the inaugural ceremonies, the machinery was 

 set in motion, the great central fountain spout- 

 ed up, and the air was filled with the sound of 

 innumerable electric bells and the peal of the 

 electric organ. This exhibition can scarcely 

 be called international, except by courtesy, for 

 the foreign exhibits did not amount to 2 per 



cent., while the exhibits from New York State 

 alone amounted to 80 per cent. Only ten years 

 before, Prof. Tyndall, during one of his lect- 

 ures, exhibited a curiosity in the form of an 

 arc-lamp. The carbons were fed by clock- 

 work; but, besides the fact that it required 

 two or three days to set up and charge the 

 battery, the mechanism was so clumsy that 

 the lamp would fail once or twice during a 

 lecture. At this exhibition, twelve engines of 

 the combined capacity of 1,800 horse-power 

 ran the dynamos that brilliantly illuminated 

 the grounds and buildings, giving in the aggre- 

 gate 1,500,000 candle-power. The two forms 

 of lamps in practical use are the arc and the 

 incandescent. The source of light in an arc- 

 lamp .is in the stream of incandescent particles 

 carried by the electric current from the posi- 

 tive to the negative pole across an interval 

 necessary to complete the circuit. The source 

 of light in an incandescent lamp resides in 

 some resisting medium, as carbon, introduced 

 into the circuit. To prevent the destruction of 

 this carbon, it must be inclosed in a vacuum. 



Are-Lamps. The exterior illumination was 

 made by arc-lamps of the Brush Company ; 

 the great lamp on the tower was said to be 

 of 100,000 candle-power. There were exhib- 

 ited arc-lamps manufactured by the Brush, 

 the United States, Fuller, Maxim, Thompson- 

 Houston, Gerard, Van Depoel, and Western 

 Companies. The difference between these va- 

 rious lamps is simply a difference of mechan- 

 ism for moving the positive carbon-rod so as 

 to keep the distance between the points of the 

 carbon-rods constant, and consequently the arc 

 of the same length and the light steady. All 

 these lamps show much perfection in mechan- 

 ism, and produce, as a rule, very steady lights. 

 There were arc-lamps mounted in numerous 

 ways for various purposes; among them, a 

 search-light, to be used on shipboard, attracted 

 a great deal of attention. The arc was formed 

 in the focus of a parabolic reflector, which could 

 be turned around a vertical axis, its intense 

 brilliancy giving great penetrating power in 

 fogs. Another arc-lamp was constructed as a 

 head-light for locomotives, and furnished with 

 a current supplied by a small dynamo in the 

 cab, run by a rotary steam-engine. The mech- 

 anism of this lamp was remarkably perfect, as 

 was necessary to give a steady light on a loco- 

 motive running at full speed. In the depart- 

 ment of arc-lighting, a lamp involving a new 

 idea was exhibited ; unlike the ordinary lamp, 

 the negative carbon, which wears away by what 

 is known as reflex action, is replaced by a point 

 of iridinm set in a wrought-iron rod and pro- 

 tected from the heat of the current. Iridiurn 

 is practically infusible, even in the intense heat 

 of the arc. A carbon is fed to this indium - 

 point through a tube by two grooved rollers 

 worked by magnets. This mechanism enables 

 the lamp to burn in any position, which is an 

 advance upon other lamps. Some specimens 

 of zircon, which may be substituted for iridi- 



