520 



NATURE 



{March 28, 1889 



much less crevassed than the Alpine, apparently due to the lesser 

 inclination of the great glaciers, and possibly to the greater 

 thickness of their ice. With reference to Caucasian forests, 

 Mr. Mummery has some interesting observations. The upper 

 valley of the Basil-su can still boast a fairly extensive forest ; 

 but partly by the axe, and mainly by the agency of the 

 sheep and goats, the forests are fast shrinking. Below a 

 certain point in the Basil-su Valley, not a tree, not a bush 

 is to be seen ; the country has been denuded by the flocks 

 of the natives. Mr. Mummery is inclined to attribute the 

 extraordinai7 contrast between the treelessness of the northern 

 valleys and the dense forests of the southern less to climatic 

 differences than to the form in which the wealth of their re- 

 spective inhabitants exists : in the one case, oxen, horses, 

 sheep, and goats ; in the other, well-tilled and neatly fenced fields 

 and orchards. Though at first sight it appears difficult to believe 

 that sheep and goats can destroy the forest over great stretches 

 of country, a careful examination of the Upper Basil-su shows 

 that the cause is sufficient to produce a continuous contraction of 

 the forest area, and leaves it a mere question of time as to when 

 the last tree in that valley shall be cut down and burnt. After 

 overcoming many difficulties, Mr. Mummery reached the summit 

 of Koshtantau, the first time the mountain had been scaled. 



Mr. Holder and his friends also succeeded in climbing Kosh- 

 tantau and several other peaks. He gave in his paper an instructive 

 account of the striking difference in the character of the moun- 

 tains which form the two great chains of the Caucasus and the 

 Alps. Mr. Holder was much impressed with the wildness, the 

 majesty, the awfulness, of the Caucasus. "Whilst the main 

 glacier streams, e.g. the Bezingi, the Mishirgi, and the Dych-su, 

 have but a slight fall, and are but little crevassed, the upper 

 parts of the glaciers, those which come down from the moun- 

 tains to form the great streams, have so steep a fall that they 

 may be compared rather to cascades than streams of ice, and are 

 cut into seracs of the most fantastic character. Comparatively 

 little snow lies on the steep southern faces of the mountains, and 

 the rocks which face the south are so broken and loose that the 

 danger of falling stones in ascending and descending is extreme. 

 No single bit of rock can be trusted, and the rope ought never 

 for a moment to be discarded. On the northern faces much 

 more snow lies, and the rocks were firmer and more reliable. 

 The climate of the Caucasus is healthy and invigorating, yet 

 distinctly more humid than in the Alps. It may perhaps be 

 sufficiently interesting to note that none of the party experienced 

 the slightest inconvenience on account of the rarity of the atmo- 

 sphere at the highest altitude reached, over 17,000 feet ; but 

 that above about 15,000 feet the snow was always of the 

 light and powdery character so tantalizing and fatiguing to 

 mountaineers. 



The March number of Petennann' s MiUeilungen contains a 

 long paper by Spiridion Gopcevic on the ethnographical condi- 

 tions of Macedonia and Old Servia. Herr Otto F. Ehlers con- 

 tributes a lively account of his ascent of Kilimanjaro last summer. 

 He does not add much to our knowledge of the mountain, nor 

 did he reach the actual summit. He went round its north face, 

 and endeavoured from the north-east side to find out the 

 character of the summit. He found the same wall of ice 

 which was seen by Dr. Meyer. He states that so far as he 

 could observe he could see no trace of a crater, while the 

 masses of ice and snow lay in quiet wave-like lines, with much 

 fresh snow. The height he estimates at over 19,690 feet. He 

 makes the extraordinary statement that traces of elephants, 

 buffaloes, and antelopes were met with at a height of about 

 16,000 feet, where also he found the last traces of vegetation. 



M. Jules Bokelli has just returned from an exploration ex- 

 tending over nearly two years in the country of Shoa and in 

 Galla Land, undertaken under the patronage of the French 

 Government. M. Borelli has added much to our knowledge of 

 Shoa and its people, and among other things has discovered the 

 source of the Hawash. His most impoitant work has, how- 

 ever, been done in the region to the south of Shoa, in the 

 country peopled mainly by the Gallas. He traced the Omo 

 River, to about 6° 20' N. lat. His map throws quite a new light 

 on the hydrography of the region. Hitherto, the Omo has been 

 conjectured to be the upper course of the Jub, which falls into 

 the Indian Ocean at the equator. But the data collected by M. 

 Borelli, and which appear to be confirmed by the recent dis- 

 coveries of Count Teleki, open the field to new hypotheses. 



It would appear that the Omo, instead of flowing towards 

 the east, takes a westerly and then a southerly direction, when, 

 at about 2° N. lat., with a breadth of over 1500 feet, it 

 expands into the great lake Samburu. It remains now to dis- 

 cover whether this lake is an African Caspian, or whether it has 

 an outflow towards Lake Victoria Nyanza. In that case the 

 Omo becomes a remote feeder of the Nile. 



ELECTRICAL NOTES. 



Nagaoka {Phil. Mag., February 1889) of the Imperial 

 University, Japan, has investigated the effects of torsion and 

 longitudinal stress on the magnetization of nickel. Stress in- 

 creases the magnetization of iron, but diminishes that of nickel, 

 and the effect of torsion is also reversed in the two metals. 

 Twisting nickel wire increases magnetization, while it diminishes 

 that of iron. Nagaoka finds that this is true for weak stresses 

 only. Beyond a critical value of the stress in a constant field, 

 one end of the nickel wire acquires the two opposite kinds of 

 magnetism during torsion and detorsion. The nickel wire used 

 was unfortunately impure, for it contained \"j per cent, of iron, 

 but the fact was clear that during untwisting the polarity of a 

 nickel wire changed sign. 



Dr. John Hopkinson, F.R.S., ha? given the Royal Society 

 (March 7) some interesting facts relating to the magnetization 

 of iron at high temperatures. At 737° C. all traces of mag^- 

 netism disappear, but before this point is reached, viz. 727°, its 

 permeability increases with great rapidity to a very high figure, 

 when it suddenly drops to unity. In a subsequent paper, read 

 March 21, he showed that the resistance also makes an abrupt 

 change at the same temperature, which is that of recalescence, 

 as discovered by Barrett. 



Shelford Bidwell (R.S., March 14) showed a very pretty 

 experiment by which the effect of radiations on the magnetiza- 

 tion of iron were made evident. An iron bar is carefully 

 annealed, cooled, magnetized, and then demagnetized by cur- 

 rents without any mechanical motion. The condensed beam 

 from an oxyhydrogen lamp is thrown upon its pole, when mag- 

 netism at once appears. There is an instantaneous magnetic 

 change, which is purely an effect of radiation. 



A. Bernstein {Centralblatt jiir Electrotechnik, i. p. 165, 

 1889) has proved that the formula Q = a ^d^ is not true for the 

 fusing currents of wires of a diameter smaller than 0*25 mm. It 

 is known that such fine wires absorb more energy than thicker 

 ones to acquire the same temperature in air, and that the formula 

 is C = ad. Bernstein has experimented with carbons of differ- 

 ent diameters in the moderate vacuum of a glow lamp, and has 

 obtained the following results : — 



Diameter in mm. Energy per sq. mm. of surface. 



0-9 0-51 



0-56 0-54 



0-29S 056 



0-185 0-85 



0-15 0.95 



His conclusion is that lamps with thick carbons absorb less 

 energy relatively than lamps with fine filaments, and are there- 

 fore more economical. 



C. S. Bowie {Electric World, February 23, 1889) has found 

 that the static electricity generated by calender rolls in a paper 

 mill acts very injuriously on the life of glow lamps. They are 

 now effectually protected with wire guards. 



Among the numerous practical purposes to which electricity 

 can be applied tanning must be added. Leather is said to be 

 produced from the raw hide in four days. 



If Prof. Oliver Lodge has failed to secure general faith in his 

 lightning conductor theories, he at least has succeeded in direct- 

 ing scientific fashion to experimenting with Leyden jars. Righi 

 {Bull. Acad, dei Lincei, xii. 16, 1888) has constructed a battery 

 of 108 condensers, having a capacity of 18,810 electrostatic 

 units. With it he has produced sparks 5 metres long over 

 strips of glass coated with zinc filings, and i metre long over 

 water. Platinum, iron, brass, gold wires, very fine and of 

 34 metres length, are instantly vaporized into beautiful coloured 

 coronse of the same shape as that impressed on the wire. The 

 wire becomes vapour at a high temperature, and forms as it 

 were a vacuum tube, the sides of which are cold air. 



