December 7, 191 1] 



NATURE 



195 



riT lalHc cubes of which J is composed. In the case of 

 culi.s on which no light is projected, nothing further will 

 happen, the charge dissipating itself in the tube ; but in 

 t\\<: case of such of those cubes as are brightly illuminated 

 by the projected image, the negative charge imparted to 

 them by the kathode rays will pass away through the 

 ionised gas along the line of the illuminating beam of light 

 until it reaches the screen L, whence the charge will travel 

 ;by means of the line wire to the plate O of the receiver. 

 I^This plate will thereby be charged ; will slightly repel the 

 'kathode rays in the receiver ; will enable these rays to 

 pass through the diaphragm P, and, impinging on the 

 fluorescent screen H, will make a spot of light. This will 

 occur in the case of each metallic cube of the screen J, 

 v.'h'rh is illuminated, while each bright spot on the 

 n H will have relatively exactly the same posi- 

 as that of the illuminated cube of J. Con- 

 sequt-ntly, as the kathode-ray beam in the transmitter 

 basses over in turn each of the metallic cubes of the 

 Bcreen J, it will indicate by a corresponding bright spot on 

 H whether the cube in J is or is not illuminated, with the 

 result that H, within one-tenth of a second, will be covered 

 with a number of luminous spots exactly corresponding to 

 the luminous image thrown on J by the lens M, to the 

 extent that this image can be reconstructed in a mosaic 

 fashion. By making the beams of kathode rays very thin, 

 by employing a very large number of very small metallic 

 cubes in the screen J, and by employing a very high rate 

 of alternation in the dynamo G, it is obvious that the 

 luminous spots on H by which the image is constituted 

 can be made very small and numerous, with the result that 

 the more these conditions are observed the more distinct 

 and accurate will be the received image. 



Furthermore, it is obvious that, by employing for the 

 fluorescent material on the screen H something that has 

 some degree of persistency in its fluorescence, it will be 

 possible to reduce the rate at which the synchronised 

 motions and impulses need take place, though this will 

 only be attained at the expense of being able to follow 

 rapid movements in the image that is being transmitted. 



It is further to be noted that as each of the metallic 

 cubes in the screen J acts as an independent photoelectric 

 cell, and is only called upon to act once in a tenth of a 

 second, the arrangement has obvious advantages over other 

 arrangements that have been suggested, in which a single 

 photoelectric cell is called upon to produce the many 

 thousands of separate impulses that are required to be 

 transmitted through the line wire per second, a condition 

 which no known form of photoelectric cell will admit of. 



Again, it may be pointed out that sluggishness on the 

 part of the metallic cubes in J or of the vapour in K, in 

 acting photoelectrically, in no wise interferes with the 

 correct transmission and reproduction of the image, pro- 

 vided all portions of the image are at rest ; and it is only 

 to the extent that portions of the image may be in motion 

 that such sluggishness can have any prejudicial effect. In 

 fact, sluggishness will only muse changes in the image to 

 appear gradually instrad r)f instantaneously. 



Many modifications are, of course, possible in detail. 

 For instance, the plate O of the receiver might perhaps 

 better be replaced by an electromagnet or solenoid so 

 arranged as to repel the kathode beam when energised, 

 .^gain, the somewhat crude form of photoelectric cell 

 described, composed merely of insulated cubes of rubidium 

 in contact with sodium vapour, might be improved upon. 

 Indr'od, it is highly probable that research will reveal much 

 more sensitive materials, the use of which would vastly 

 Improve this part of the apparatus, which at present is 

 probably the one least likely to give the desired results. 



GEOGRAPHY OF BRITISH CEXTRAL AFRICA."^ 

 A TTENTION was first directed to " British Central 

 Africa " by Dr. Livingstone in 1859. ^y the term 

 " British Central .\frica " I mean the present protectorate 

 of " Nyasaland," together with north-eastern Rhodesia; 

 that is, the British territory bordering on the Shire River, 

 and on Lakes Xyas,'i, Tanganyika, Mweru, and Bangweulu. 



1 From a paper on "The Geoijraphy and Economic Development of 

 British Central Afric.i," read before the Royal Geographical Society on 

 December 4, by Sir Alfred Sharpe, K.C.M.G., C.B. 



NO. 2197, VOL. 88] 



Records show that the Portuguese had some knowledge 

 of the Nyasa regions so far back as the seventeenth century, 

 though they never established any stations there. They 

 followed the line of " least resistance," the Zambezi River, 

 which was navigable for small craft up to the Kebrabasa 

 rapids. It may be taken as practically certain that at the 

 very ancient period when at " Zimbaw'e " and elsewhere in 

 Mashonaland there existed a flourishing gold-producing 

 industry, the River Zambezi was known and navigated by 

 the same ships which brought traders to the port of Sofala'. 

 No ancient lock-workings for gold have been found north 

 of the Zambezi similar to those in Mashonaland, but it is 

 not improbable that the traders of those days obtained 

 copper from Katanga, and used the Zambezi as their most 

 available transport route. With regard to the ruins in 

 Mashonaland, no African race unaided ever erected these 

 stone buildings, nor, in my opinion, can they be dated back 

 to anything but the most ancient times. ' The idea that 

 Solomon got his gold there has sometimes been ridiculed ; 

 but why not? We know that in those times fleets were 

 sent out from the Red Sea periodically, which returned with 

 gold, apes, ivory, and feathers — all products of Africa. 

 These ships were probably identical with the Red Sea dhows 

 of to-day. Where would explorers with vessels of that type 

 be likely to go first, on leaving the Red Sea? Out into the 

 Indian Ocean? or down the African coast? They would, of 

 course, follow down the land ; and whether or not in King 

 Solomon's days he got his gold from the east or the south, 

 it may be taken as certain that the whole East African 

 coast was then known and frequented by traders. It is 

 interesting to note that the question as to who were the 

 ancient people who worked the gold-mines of South-east 

 Africa is no new one. In that fascinating book, " A 

 History of Africa," by John Ogilby, published in 1670, the 

 matter is thoroughly discussed, and the arguments for and 

 against King Solomon are fairly stated. Ogilby says, in 

 speaking of the kingdom of Monomotapa : "In this 

 country far to the inland on a plain stands a famous 

 structure called Zimbawe, built square like a castle with 

 hewn stones of a wonderful bigness. Above the gate 

 appears an inscription which cannot be read or understood, 

 nor could any that had seen it know what people used such 

 letters. Near this place are more such buildings by the 

 same name, signifying a court or palace. The inhabitants 

 report it a work of the devil, themselves only building with 

 wood." Also, as regards Sofala, he says: "The inhabit- 

 ants aver that this is the very true Ophir from whence King 

 Solomon had his gold." Then follows a full statement of 

 the arguments pro and con. 



The geographical position of Nyasaland is a somewhat 

 remarkable one. The Shire valley and Nyasa form the 

 southern portion of one of the greatest " rifts " in the 

 African continent. This depression, after a break north of 

 the lake, is carried on for 400 miles by Lakes Rukwa and 

 Tanganyika, and, with a few short breaks, runs on by 

 Lakes Kivu, Albert Edward, and Albert, to the Nile valley. 

 Following this route, a journey by boat could be made 

 from the mouth of the Zambezi to the Mediterranean, a 

 distance of more than 4500 miles, covering 50 degrees of 

 latitude, with a total distance of land portages of not more 

 than 500 miles. A curious point about this great lino of 

 depression is that for a great part of its length it lies 

 almost alongside the backbone of tropical Africa, the water- 

 shed in some parts approaching within a few miles of the 

 lakes which lie along its course. 



Most of British Central Africa has an average elevation 

 of some 3000 to 4000 feet above sea-Icvel. Here and there 

 are higher plateau masses and peaks, which in some casos 

 rise to close on 10,000 feet. The most notable of these 

 plateaux are " Nvika " in the North Nyasa district and 

 " Mlanje " in the Shire Highlands. The former has an 

 average altitude of 7000 to 8000 fcet^ with an area of 

 2000 square miles, and a European climate ; the Mlanje 

 plateau lies at 6000 to 7000 feet, and has an area of some 

 2;o square miles. Both are what Sir Harry Johnston used 

 to rill " Jack and the Beanstalk " countries, the plateau 

 -■(1(-; 1 i^ing precipitously from the surrounding country, and 

 l.( iim .ilniost unclimbable. On Mlanje grows the Widdriiiff- 

 Innni -..'livtci (Mlanje cypress), a large handsome conifer, a 

 v( 1 V \;i!unhlo timber of excellent quality, durable and 

 imiii rv! >!i~ f'l the attacks of white ants. 



