378 



NATURE 



[February i6, 1893 



Selous to successfully guide the Pioneer Force of the Chartered 

 Company in 1890, when they took possession of Mashonaland. 



With regard to the health of Zambesia he says : — " Owing 

 to severe exposure to wet and cold during several days and 

 nights, in the early part of 1872, I got an attack of fever and 

 ague in Griqualand so that I was handicapped before starting 

 for the interior. This fever and ague was exactly what I have 

 seen people get on the high plateau of Mashonaland, during the 

 last few years, from similar exposure to rain and cold. It took 

 me some time to shake off, and was still in my system when I 

 reached Matabeleland, but the attacks only came on when I 

 halted anywhere for a lew days. During November and 

 December, 1872, hunting down in the low hot country towards 

 the Zambesi, I was again very much exposed to wet, and on 

 several occasions lay out all night long, without any shelter, 

 drenched through with such heavy rain that it put out the largest 

 fire and converted hard ground into a swamp. I naturally again 

 ;jot soaked with fever poison, but as long as I remained 

 hunting the disease did not show itself. Directly I got back 10 

 Bulawayo it broke out, and during a month or so I had several 

 sharp attacks. By that time, however, my sound constitution 

 had choked all the fever germs, and from that day until in 1878, 

 when very severe exposure in Central Africa once more filled 

 me up with malarial poison, I do not remember ever to have 

 had one single hour's illness, or to have taken one drop of medi- 

 cine. The life I led was, however, if a very hard, at any rate, 

 in many respects, a very healthy one ; for the most part I ate 

 nothing but meat and Mashona rice, and drank nothing but 

 tea, usually without milk and sugar — not because I like it so, 

 but because those adjuncts were unobtainable. " 



North of the Zambesi Mr. Selous made several journeys among 

 the Batongas, and spent a wretched rainy season, almost with- 

 out equipment, on the Manica table-land. After the rains the 

 country looked charming. The young grass,- thanks to the re- 

 cent heavy rain, had shot up one foot or eighteen inches in height 

 over hill and dale, every tree and shrub was in full leaf, and 

 everything looked green, and fresh, and smiling. Many of the 

 shrubs on the edge of the hills bore sweet-smelling flowers, and, 

 as on all the plateaus of the interior of Africa, small but beauti- 

 ful ground-flowers were very abundant. 



Interesting observations were made on some of the northern 

 rivers. The curious phenomenon of the steady rise of the waters 

 of the Chobe and Machabi — an outlet of the Okavango— was 

 observed from the first week in June until the last week in Sep- 

 tember, when they commenced "to recede. That the Okavango 

 and the Upper Kwando are connected on their upper courses, 

 there can be little doubt, as the waters of the Machabi went on 

 rising suddenly /(rrz/a^vw with the Chobe, until the end of Sep- 

 tember, when both commenced to recede simultaneously. 



The explanation of this remarkable phenomenon is difficult, 

 as there are no snow mountains at the sources of the Kwando 

 and Okavango rivers and the Zambesi, which rises in the same 

 latitude, decreases steadily in volume from day to day during the 

 dry season like almost all other rivers in South Central Africa. 

 Besides the channels which still become annually filled with 

 water from the overflow of the Chobe and Okavango river sys- 

 tems, there are many others which are now quite dry, but in 

 which the natives say they once used to travel in canoes. j 



From 1882 the journeys acquired additional geographical 1 

 importance, and Mr. Selous proceeded to rectify the maps of 

 Mashonaland laid down by earlier travellers, taking constant ( 

 compass bearings, sketching the course of rivers, and fixing the 

 position of the junction of tributaries. The value of this work 

 was made manifest in a magnificent large scale map of the 

 country, drawn as well as surveyed by Mr. Selous, which was 

 used to illustrate the lecture. It would be impossible, without 

 practically reproducing the whole address, to do justice to the 

 immense variety and solid value of the contributions to African 

 geography made by this most energetic of pioneers ; or to the 

 thrilling adventures, the recital of which was listened to with | 

 breathless attention and greeted with the heartiest applause. 

 With the exception of a treacherous night attack made upon his 

 camp by the Mashuku-sumbwe, led by a few rebel Marotse, in 

 1888, he had never had any other serious trouble with the natives. 

 During his twenty years' wanderings he went amongst many 

 tribes who had never previously seen a white man, and he was 

 always absolutely in their power, as he seldom had more than 

 from five to ten native servants, none of whom were ever 

 armed. 



NO. 1216. VOL. 47] 



THE DISTRIBUTION OF POWER BY 



ELECTRICITY FROM A CENTRAL GENERA T- 



ING STATION. 



r^N Friday evening, the 3rd inst., Mr. A. Siemens delivered at 

 the Royal Institution an interesting lecture on the ways in 

 which science is applied to practice. In the course of the lecture 

 he made the following remarks on the distribution of power by 

 electricity from a central generating station : — 



Before entering further into this, let me remind you that the 

 earliest magneto-electric machines were used nearly sixty years 

 ago for the production of power. I will mention only Jacobi's 

 electric launch of 1835 as an example. It must, therefore, be 

 considered altogether erroneous to ascribe the invention of the 

 transmission of power to an ac:ident at the Vienna Exhibition 

 in 1873, when, it is said, an attendant placed some stray wires 

 into the terminals of a dynamo machine ; it began to turn, and 

 the transmission of power was first demonstrated. As a matter 

 of fact. Sir Wm. Siemens once informed me, that his brother 

 Werner was led to the discovery of the dynamo-electric principle 

 by the consideration that an electro-magnetic machine behaved 

 like a magneto-electric machine, when a current of electricity 

 was sent into it, viz. both turn round and give out power. It 

 was, of course, well known that a magneto-electric machine 

 produces a current of electricity, when turned by mechanical 

 power, and Werner concluded that an electro-magnetic machine 

 would behave in the same manner. We all know that he was 

 right, but I relate this circumstance only as a further proof that 

 the generation of power by electric currents has been a well- 

 known fact long previous to the Vienna Exhibition. 



Another well-known instance of transmission of power to a 

 distance is furnished by the magneto-electric ABC telegraph 

 instruments, where the motion at the sending end supplies the 

 currents necessary to move the indicator at the receiving station. 



As an illustration of the distribution of power by electricity, I 

 will briefly describe some radical alterations that have been made 

 at the works of Messrs. Siemens Brothers and Co., by the intro- 

 diiction of electric motors in the place of steam engines. 



[A diagram on the wall showed in outline the various buildings 

 in which work of different kinds is carried on with the help of 

 different machines.] 



Electric motors are supplying the power, sometimes by dri- 

 ving shafting to which a group of tools is connected by belting, 

 and sometimes by being coupled direct to the moving mechanism. 

 Each section of the works has its own meter, measuring 

 the energy that is used there, and all of them are connected by 

 underground cables to a central station, where three sets of 

 engines and dynamos generate the electric current for all purposes. 

 There are two Willans and one Belliss steam engines, each of 

 300 horse-power, coupled direct to the dynamos, and running at 

 a speed of 350 revolutions per minute. Room is left for a 

 fourth set, but including some auxiliary pumps and the switch- 

 boards for controlling the dynamos and for distributing the cur- 

 rent, the whole space occupied by 1260 horse-power measures 

 only 32 X 42 feet. Close by are the condensers and three high- 

 pressure boilers, which have replaced some low-pressure ones 

 formerly used for some steam engines driving the machinery in 

 the nearest building. 



The advantages that have been secured by the introduction of 

 electric motors may be briefly stated under the following 

 heads : — 



1. Various valuable .spaces formerly occupied by steam engines 

 and boilers have been made available for the extension of work- 

 shops, and these are indicated on the diagram by shading. 



2. By abolishing to a great extent the mechanical transmission 

 of power a considerable saving is effected in motive power, 

 which is especially noticeable at times when part only of the 

 machinery is in use. 



3. As the electric motors take only as much current as is actu- 

 ally required for the work they are doing, a further saving is 

 effected, and at the same time the facility with which the speed 

 of the motors can be altered without their interfering with each 

 other presents a feature that is absent from mechanical trans- 

 mission. 



4. The big steam engines being compound and condensing, 

 produce a horse-power with a smaller consumption of fuel than 

 the small high-pressure steam engines scattered throughout the 

 works. 



