194 



NA TURE 



[July i, 1897 



The principal geological problem, which it was hoped 

 the expedition would settle, was whether the Omo Valley 

 is a continuation of the great East African Rift Valley, 

 in which Lake Rudolf lies. Unfortunately the circum- 

 stances which prevented Dr. Smith tracking the Nianam 

 further towards its source are responsible for this ques- 

 tion being left open. Ur. Smith, however, believes that 

 the Omo is one of the head streams of the Juba, and does 

 not flow into Lake Rudolf, as is generally believed from 

 Borelli's work. If the altitudes given us are correct, the 

 new view is impossible. Borelli descended the Omo to the 

 level of 3450 feet : Bottego ascended the Juba to a height 

 of over 4500 feet : the Omo cannot flow looo feet up 

 hill into the Juba. Another alternative was once pos- 

 sible. We have previously suggested, from Dr. Smith's 

 preliminary map, that " it is just possible that the Omo 

 reaches this lake [Abaya] instead of Basso Narok [z>.. 

 Lake Rudolf]" [Gregory, "Great Rift Valley," p. 258]; 

 but now Dr. Smith fixes the height of Lake Abaya as 

 3460 feet, so that the Omo is excluded from that goal. 

 Hence, we are driven to the conclusion that the Omo 

 must continue as the Nianam, and flow into Lake Rudolf, 

 as Borelli believed ; this conclusion is in agreement with 

 the altitudes and with the trend of the country as shown 

 by Dr. Smith's map. 



Another point of interest to geologists is the evidence 

 as to the existence of volcanic activity in this region ; for 

 Dr. Smith tells us that the Teleki volcano at the southern 

 end of Lake Rudolf, in August 1895 "sent up clouds of 

 smoke, and at night a great stream of glowing lava could 

 b2 seen pouring from one of the craters " (p. 333). This 

 information is especially interesting, as Mr. Neumann 

 found no signs of activity there, and as the oft-asserted 

 " Volcano Doenyo Ngai " now turns out not to be a true 

 volcano. 



In one respect Dr. Smith's information is strikingly 

 different from that of Teleki and Hohnel. These ex- 

 plorers found the water of Lake Rudolf so brackish that 

 they could hardly drink it, while that of Lake Stefanie was 

 so salt that it was quite useless, and they could only stay 

 on its shore owing to the existence of pools of rain-water. 

 This was in 1888. But in 1895 I^*"- Smith found the 

 water of both lakes was quite fresh, in which he is con- 

 firmed by a very accurate observer, Mr. A. H. Neumann, 

 for the northern end of Lake Rudolf. There can be no 

 doubt that a remarkable change in the salinity of these 

 lakes has taken place in only seven years ; and the possi- 

 bility of such changes must be borne in mind in consider- 

 ing the origin and relations of the African lake faunas. 

 For example, it has been urged that the marine origin of 

 the Tanganyika fauna is impossible, since there is no 

 trace of marine influence in that of Lake Nyasa, through 

 which the former, on the usual theory, must have passed. 

 But Lake Stefanie reminds us that either a too rapid 

 freshening of a lake, or a period of intense salinity, may 

 obliterate the original fauna. Hence the complete absence 

 of any marine types from the fauna of Nyasa is no 

 proof that that of Tanganyika had not a marine origin. 

 It should, however, be remarked that we are not express- 

 ing any acceptance of the view that the fauna of Tan- 

 ganyika has any marine characters ; but only that one 

 of the arguments against that view is invalid. 



The part of the book most open to criticism is that 

 NO. 1444. ^0\.. 56] 



dealing with ethnography ; but the facts mentioned show 

 that the country traversed is of extreme interest. The 

 author found some dwarf people about five feet high, and 

 gives us a list of their words, although a few phrases 

 would have been, more useful ; he describes some wells, 

 which he attributes to the ancient Egyptians : and he met 

 with Midgans, Tpmal and "half-caste Boran," respecting 

 each of which more detailed information is desirable. 

 One quaint slip in this department is speaking of a 

 " tamasho isic) or equestrian exhibition " as though it were 

 a Somali word instead of Hindustani for a " function. ' 

 But one man cannot do everything ; and now that the 

 author has shown the way, we hope that other travellers 

 will follow and collect further information regarding the 

 many questions which the volume raises. For it is a great 

 testimony to the interest of the country that Dr. Donaldson 

 Smith's valuable book suggests as many problems as it 

 solves. J. W. G. 



EXERCISES IN PHYSICS. , 

 Problems and Questions in Physics. By C. P. Matthews 

 and J. Shearer. Pp. vii-F247. (London: Macmillan 

 and Co., Ltd., 1897.) 



THIS useful book contains more than thirteen hundred 

 problems in the various branches of physics, and, 

 from the point of view of degree work, covers the ground 

 required for the London Matriculation and Intermediate 

 Science Examinations, as well as part of that for the 

 Final B.Sc. It is, however, intended for all students of 

 elementary physics, includmg, therefore, students of 

 engineering, and the peculiar needs of the latter have 

 also been provided for. 



The authors begin with an introduction, which, as 

 they explain, is intended not only to be read, but con- 

 tinually referred to, and contains short sections on 

 physical measurement in general, units, vectors, the ex- 

 pression of physical relations by curves, averages, and 

 approximations. A few examples are added on graphic 

 methods, as well as a list of units and physical con- 

 stants for use in the problems. Next follow the pro- 

 blems themselves ; and the book ends with a set of four- 

 figure mathematical tables, the solutions to the problems, 

 and a rather meagre index. 



In a work designed for students of both engineering 

 and physics, one naturally looks first to see what is said 

 on the vexed question of the unit of force. We con- 

 gratulate the authors on the line they have here taken. 

 As they explain in their preface, 



" Many of the students who will use these problems 

 are pursuing engineering courses. In such case, they 

 must of necessity use engineering units. The aim has 

 been not so much to train them in the use of these units 

 — an abundance of this training comes to them during 

 their course — but to bring out the relation of the so-called 

 practical and gravitational units to the C.G.S. units of 

 physics." 



The C.G.S. and foot-pound-second systems are first de- 

 fined, and the superfluous character of the latter tacitly 

 assumed. This is shown by the fact that, after its 

 definition has been given, the word poundal does not 

 again occur. The authors then explain that pound and 

 kilogramme are used by engineers as names for units of 



