92 



SCIENCE. 



[Vol. XI. No. 264 



Tibetan blankets, musk-pods, goats, ponies, clarified butter, and 

 yak-tails. The chief grain grown is maize or Indian-corn. The 

 domestic animals comprise buffaloes, yaks, zobus (cross-breed 

 between yak and cow), goats, and sheep of the long-horned species, 

 largely used in Tibet for transport purposes. The yak and female 

 zobu afford a plentiful supply of milk. Among the wild fauna are 

 musk deer and Tibetan antelopes, while flocks of wild pigeons and 

 ravens and pheasants are common. 



" The Daibung was away when the explorer reached Dingri, and 

 did not return till Oct. 21. Great trouble was experienced in get- 

 ting him to accord permission for the party to proceed westwards. 

 The Daibung declared that this route was absolutely closed to all 

 but officials; but in consideration of the explorer's companion, who 

 was a man of influence in these parts, and in consideration of his 

 promise to be answerable for their good behavior, the required per- 

 mission was granted, but with a proviso that from village to village 

 a guide should escort the party and send back regular reports of 

 the progress made. 



" The general direction of the explorer's route then trended to 

 the west, past the Palgucho Lake, about nine miles by four in e.x- 

 tent, the waters of which are clear and sweet to the taste, though 

 it has no outlet. The Tibetan fort of Jonkhajong, the farthest 

 point to the north-west reached, is a substantial stronghold, about 

 four hundred paces square, protected by a mud and stone wall. 

 Two officials, called Jongpons (Tib. = 'governor of a district ') re- 

 side here, and exercise civil and judicial authority short of capital pun- 

 ishment. The surrounding country appeared well cultivated, and the 

 inhabitants were reaping their harvest at the time. The Jongpons 

 gave permission for the party to travel to Nubri in accordance with 

 the terms of the passport, but, as the route was reported to be 

 closed by heavy falls of snow, it was only by more presents that a 

 pass allowing M — H to proceed as far as Kirong was obtained. 

 Beyond Kirong the route nears the river, and for about one hun- 

 dred paces is carried over a gallery about six feet wide, run along 

 the perpendicular face of the rock at a height of from fifteen to 

 twenty feet above the water's edge. The gallery rests on thick 

 iron bolts driven into the rock at intervals, over which planking is 

 loosely laid : the outer edge is fenced by a rudely made rope passed 

 round wooden posts fixed to the bolts. At Naiakot the route turned 

 westwards, and, crossing the watershed of the Tirsuli River, de- 

 scended into the valley of the Buri Gunduk, one of the chief rivers 

 of Nepaul, which M — H ascended as far as Nubri, along a route 

 nearly parallel with the line of his southward journey. Thence he 

 retraced his steps along the Buri Gunduk to Arughat, a Nepaulese 

 , village, where the party were detained three days pending the result 

 of inquiries as to whence they had come and for what purpose. 

 The explorer professed to have gone all the way to Nubri in search 

 of one of his dependants, who, he alleged, had run away from 

 M — H's home in Jumla with a large sum of money some time 

 before, but whom he had not succeeded in finding. He said that, 

 having failed in his object, he was anxious to return home vid Tir- 

 beni, where he intended going through the customary religious 

 observances. He was then allowed to proceed, but warned, that, 

 owing to the disturbed state of the country consequent on the recent 

 insurrection in Khatmandu, he was liable to detention in several 

 places. His further route to Tirbenighat, on the British frontier, 

 lay in a south-westerly direction." 



ELECTRICAL SCIENCE. 



Alternating Current Electro-Motors.' 



The alternating system of electrical distribution possesses many 

 advantages for distributing electrical energy over extended areas ; 

 it has, however, certain disadvantages, among others that of not at 

 present allowing the use of electric motors for the distribution of 

 power. 



In any central station supplying electric lights the full capacity 

 of the plant is utilized but a short time during the twenty-four 

 hours, and, taking the whole day, we will find that we have sold 

 an amount of energy equal to a half or a third — perhaps even less 



— of the amount we could supply supposing we worked always at 

 full capacity. ^ 



If we draw a curve representing the energy used at different 

 hours of the day for lighting, it will be something like O D E H F 

 G X'm Fig. I. The total amount we could have sold is .4 O X B. 

 If we can use motors on the circuit, we can sell an additional 

 amount of power such that the power used for lighting and by the 

 motors never exceeds the maximum capacity of the station. For 

 instance, if the motors work until 6 p.m., we can use for them a 

 horse-power equal to HI, and the total energy we can sell for the 

 motors is ////if Z.. The solid part of our diagram is all of the 

 energy that a purely alternating system can expect to utilize : a 

 continuous current system, by employing storage-batteries, could 

 fill the whole of the area A O X B. 



In the alternating system the current and electro-motive force 

 may be represented by the curves 1 and II, Fig. 2. the maximum 



value of the current lagging behind the maximum of the electro- 

 motive force. In the main circuit a high electro-motive force of 

 constant maximum value is used, and this is reduced at points of 

 consumption to the low potential necessary for safety, and for use 

 with incandescent lamps, by ' transformers ; ' that is, by ' induction- 

 coils ' working backward. The value of the system lies in this : by 

 using high potentials in the main or primary circuit, we can trans- 

 mit a great deal of energj' with comparatively little current, and 

 therefore with little loss in the lines. This enables us to use 

 small conductors, and avoid the large investment in copper neces- 

 sary in distributing energy by the direct system. 



If we can use motors in this system, we can almost double our 

 receipts with comparatively little increase in our expenses. The 

 plant rem^yns the same ; the salaries, interest on investment, and 

 depreciation, are only slightly increased ; our main additional ex- 

 pense is for the fuel. 



The forms of motors that can be run by alternating currents are 

 (i) an ordinary series-wound motor; (2) a motor built like an alter- 

 nating current dynamo, ttie field-magnets being excited by the 



1 Abstract of a paper read before the A 

 Dr. Louis Duncan, Johns Hopkins Unive 



Institute of Electrical Eng 



alternating current, which is first commutated so that its direction 

 is always the same ; (3) the same arrangement as the last, except 

 that the field-magnets are excited by a continuous current from 

 some external source ; (4) the form proposed by Prof. E. Thomson, 

 in which the armature currents are not supplied from any external 

 source, but are induced in them by the alternations of the field- 

 current. 



Of these forms, (3) appears the most promising. Its advantages 

 are, that when it is once started it will perfectly govern itself, re- 

 volving at such a speed that its own reversals of electro-motive force 

 occur with the same rapidity as those of the dynamo driving it ; it 

 is cheap to construct, and durable ; and it should be efficient, and give 

 a greater output than corresponding machines of the other types. 

 Its disadvantages are, that it must be first driven to its proper 

 number of revolutions before the alternating currents will run it ; 

 there must be some external source of continuous current to excite 

 the field-magnets ; and if a load possessing any considerable inertia 

 be suddenly applied, the motor will stop. 



It is proposed to avoid these difficulties in the following way: 



