December 28, 1888.] 



SCIENCE. 



started and stopped without the use of brakes in the space of three 

 or four inches, and, when making the normal running speed, can, 

 in an emergency, be stopped and reversed without brakes within 

 less than a quarter of a car length. This is especially advanta- 

 geous in crowded thoroughfares, and shows the superiority of the 

 electrical car over the horse or cable cars. The control over the 

 car seems marvellous, for one sees little or nothing save an almost 

 imperceptible movement of the hand of the motor-man ; and the 

 starting, although prompt, is very gradual and without shock or jar- 

 The ordinary driver can operate one of these cars without the slight- 

 est trouble, after a very brief instruction. The saving on the oper- 

 ating cost of the Sprague system, owing to the superior quality of 

 the apparatus, over an ordinary horse-car line, constitutes a no in- 

 considerable item. It has been found that the average cost of 

 motive power per car a day throughout the United States — that is, 

 for from ten to eleven hours, and trips aggregating from forty-live 

 to fifty miles — is about four dollars, and this counts only those 

 horses on actual duty on the road. The cost of motive power per 

 day per car for equal mileage in Richmond is less than two dollars 

 on the heaviest sort of grade-work, and at Boston it is estimated 

 that even this low cost of operation will be reduced. For winter 

 use upon this road the Sprague Company is equipping three elec- 

 tric 'working-cars,' furnished with snow-ploughs, brushes, ice-cutter. 



In switching, two ordinary tongue-switches are used, — one in 

 the conduit, and one on the rail. Brushes attached to the snow- 

 ploughs and cars easily kee]) the conduit and tracks clear, even in 

 the severest snow-storm or in case of slushy and muddy weather. 



The change from the overhead system to the conduit is made 

 while the car is in motion, and without the slightest delay in travel 

 or inconvenience to passengers; so that the Sprague cars run over 

 the entire distance. 



The kind of truck used upon this road is the latest Sprague im- 

 proved truck, which has been fully described in these columns. 

 The e(|uipmcnt of this truck includes the new Sprague ' Boston ' 

 motor, which will be used, for the first time in commercial work, 

 upon this road. 



MOHAMMEDANISM AND SLAVE-TRADE IN AFRICA. 

 The recent events in Africa have shown the enormous power 

 Mohammedanism e.xerts in that continent. The growth of the 

 empire of the Mahdi, the foundation of states by the Fulbe, the 

 steady progress of Mohammedanism in the Galla country, prove its 

 vast historical importance in Africa. We have shown on the ac- 

 companying map the distribution and growth of Mohammedan 

 power in Africa according to an interesting study by A. Oppel, 

 published in the Journal of the Geographical Society of Berlin. 



and salt-distributer, and each propelled by two powerful 30-horse- 

 power motors. In front of the car is a revolving wheel which 

 breaks up the snow-crust completely, and behind are revolving 

 brushes which sweep the tracks clean. It is estimated that this 

 ' working-car ' will clear a street-railway track after a heavy storm 

 more quickly than the ordinary snow-plough drawn by 12 horses. 



The system of wiring which the West End management has 

 adopted for the crowded city streets is the Bentley- Knight conduit, 

 now in use in Allegheny City, Penn. Here the conduit is laid mid- 

 way between the tracks, and is strongly bolted to the stringers and 

 sleepers. Its cross-section is about a foot square, and its upper 

 part has a slot similar to that used in cable- railways ; its width, 

 however, being only five-eighths of an inch, giving an opening so 

 small that carriage-wheels will not catch in it. Besides this, it is so 

 bevelled that horseshoe calks will not be held in it. Copper bars 

 an inch and a quarter thick, one on each side of the slot, firmly in- 

 sulated beneath it, carry the current, — one from the dynamo, and 

 the other returning from the motors. The current is taken from 

 the conductors to the motors by ' ploughs,' as they are called, two 

 to each car. These ploughs are thin iron plates about ten inches 

 square, hung from a framework over the middle of the track, and 

 projecting into the slot. The motors are connected by controlling- 

 switches, and the car is operated substantially as is the overhead 

 system. The ploughs are so arranged that they can be lifted out 

 of the slot when any obstruction is reached. The current is taken 

 up and returned by spring-plates, which slide along the copper con- 

 ductors at the bottom of the plough. 



Christianity early penetrated into Egy-pt, and from this point 

 spread rapidly up the Nile as far as Abyssinia, and all over the 

 north coast of the continent. In Egypt many of its dogmas were 

 developed under the influence of Ale.xandrinian philosophy, while 

 some of the ceremonies of ancient Egyptian worship found their 

 way into the Christian cult. Here, also, many dogmatic contro- 

 versies originated, which were the cause of long-continued wars. 

 The Christian Churcli in Africa disintegrated, and at the same 

 time was degraded by assimilating numerous heathenish elements. 

 When, therefore, Mohammedanism first entered .\frican territory, 

 the ancient Christianism was swept away. In 640 A.D., Omar's 

 general, .-\mru Ibn al Assi. invaded Egj'pt, which had been a prov- 

 ince of Byzantium, and in 641 conquered Alexandria. In order to 

 secure his hold upon the newly conquered province. Omar settled 

 a number of Arabian tribes in Egypt, and through their influence 

 numerous natives adopted the Mohammedan faith. Amru next 

 subjected the western borderland of Egypt, and his successor, in 

 664, conquered Fezzan. In 711 the whole of North Africa was 

 under Arabian sway. The native Berbers as well as the descend- 

 ants of the Greeks and Romans, soon adopted their faith and lan- 

 guage. 



In the sixteenth century the power of the Berbers had increased 

 considerably, and by acknowledging the authority of a Berber 

 caliph they became independent of the Oriental Empire. As the 

 number of Arab immigrants was originally small, they began to 

 be merged into the Berbers : but in the middle of the eleventh 

 century several nomadic tribes who had lived in upper Egypt 



