August 20, 1896] 



A^A TURE 



373 



two ranges, and the similarity of conditions affecting the 

 Caucasus and the southern Urals, the various progressive 

 stages of erosive action are carefully traced, and the results 

 taken to illustrate a number of important points in the new 

 science of geomorphology, especially in connection with such 

 examples as the Alleghany Mountains, and the extinct range 

 known to geologists as the "Central German Alps," which now 

 forms the Thuringian and Black Forests, and the Harz. 



The Geodynamic Section of the Meteorological Observatory 

 of Constantinople has just completed the publication of its first 

 year's work, and in the last monthly Biillclin (for December 

 1S95) 'l^s Director, Dr. -Vgamennone, summarises the results. 

 The area studied is not confined to the Ottoman Empire, but 

 includes all the countries bordering the eastern end of the 

 .Mediterranean. Nevertheless, out of 753 shocks recorded in 

 the Btilktiiis (an average of more than two per day), 400 belong 

 to Turkey ; while 236 occurred in Greece, and 55 in Bulgaria. 

 (Jf the (ireek earthquakes, more than two-thirds were felt in 

 the island of Zante. From Persia, the Caucasus, and the region 

 beyond the Caspian Sea, the reports are fesv in number, but this 

 is probably owing to the want of observers. The slight shocks 

 of course greatly predominate, amounting to 519; 225 were 

 strong, or very strong, and nine disastrous. Most of the records 

 are very brief, but more detailed accounts are given of four 

 earthquakes — those of the Caspian Sea on July 9, the Adriatic 

 Sea on August 9, Pergama on November 13-14, and Salonica 

 on December 2. The value of Dr. Aganiennone's work will be 

 evident when we compare this ample chronicle with the list of 

 49 shocks in the Ottoman Empire during the previous year. 



The difficulty of recognising the direction from which a 

 sound proceeds is a well-known obstacle to the full utilisation 

 of acoustic signals at sea. It often happens that a gun signal, 

 or especially a steam whistle, is supposed by one of the watch to 

 be on the port side, while another hears it to starboard. M. E. 

 Hardy, in La Nature, describes an apparatus which should 

 prove effective for determining the direction of the sound waves. 

 Two microphones are placed on board at as large a distance 

 apart as possible, say 100 yards. Each of the microphones is 

 connected with a telephone. The observer holds the forward 

 telephone to his right ear, and the stern telephone to his left. 

 Then, when a signal is given by a vessel straight ahead, he will 

 hear it first in his right ear and then in his left, and the interval 

 will be that required by the sound wave to travel from one 

 microphone to the other. In the case supposed, the interval 

 will be alxjut one-third of a second. When the strange vessel 

 is just abeam, the sounds will strike the microphones at the same 

 instant, and the observer will hear them as coincident. When 

 it is just astern, the left ear will be the first 10 hear the signal. 

 This method, while capable of fi.xing the angle between the 

 keel of the vessel and the direction of the stranger, does not 

 decide the port-or-starboard question. This might be done by 

 a similar auxiliary apparatus amidships. Another method de- 

 scribed by the same author is based upon the interference of 

 sound waves, the sound being received by a tube dividing into 

 two branches whose ends are placed at a distance apail equal to 

 half the length of the sound wave, and are attached to the ends 

 of a bar capable of rotating in a horizontal plane. When this 

 bar points in the direction whence the wave proceeds, and only 

 then, will the sound heard through the lube vanish by inter- 

 ference. But the wave may be proceeding along the bar either 

 forwards or backwards, so that here again we have an ambiguitj-. 

 But it must be borne in mind that the choice between two 

 exactly opposite directions is comparatively easy. Considering 

 the differences of pitch of the various bells, whistles, and fog- 

 horns in use, we should prefer the first method. But the sound 

 NO. 1 399, VOL. 54] 



rays rarely proceed in straight lines from the source, and 

 there are many objective difficulties besides the subjective one 

 mentioned. 



In the May number of the Records of the Indian N.W. 

 Geological Survey, Dr. W. T. Blanford sums up the results of 

 recent investigations on the ancient geography of Gondwana- 

 land, the great southern continent of which Australia, peninsular 

 India, Southern Africa anil South America are the now isolated 

 remnants. He points out how, one by one, each of these great 

 southern land-masses has been found to contain remains of the 

 peculiar Gondwana flora so difierent from the contemporaneous 

 (Carboniferous and early Mesozoic) floras of the northern hemi- 

 sphere, and how in each case a peculiar boulder-bed, accom- 

 panied by unquestionable evidence of its glacial origin, has been 

 found associated with them. Recent discoveries in South 

 America have completed the chain of resemblance, and show 

 the great e.xtent of the Gondwana continent. At the same time, 

 if the South American boulder-bed be as truly glacial as that of 

 the other areas, any attempt to explain the occurrence of this 

 glaciation within the Tropics by a shifting of the earth's axis 

 must be finally abandoned. It does not necessarily follow that 

 an unbroken continental tract extended at one and the. same 

 time from South America through Africa and India to Australia, 

 but the whole region must at least have been mainly land, at a 

 time when the Pacific Ocean was already as important a terres- 

 trial feature as it is now. This continental mass, too, with its 

 peculiar flora, must have been separated from the northern 

 lands, on which the Lepidodendron and Sigillaria of our coal- 

 measures flourished, by some barrier, probably the Tethyan 

 Ocean of Suess, of which our present Mediterranean and 

 Caribbean seas are the shrunken remnants. Two recently 

 recorded facts of hydrography are mentioned by Dr. Blanford, 

 as throwing an interesting side-light on the difference now 

 existing between the ancient basin of the Pacific and the modern 

 oceans which occupy part of the site of Gondwana-land. The 

 first is the much slower rate at which the Krakatoa wave of 1883 

 was propagated through the shallower waters of the South 

 Atlantic than through the deep Pacific. The other is the warm 

 temperature of the bottom-waters of the North-west Indian 

 Ocean, which indicates that they (like those of the Mediter- 

 ranean) are isolated by some barrier from the cold bottom- 

 currents, and such a barrier must run in precisely the direction 

 required for the ancient connection of India and Southern Africa. 

 Thus evidence from all directions converges to indicate the 

 fundamental difference between Atlantic and Pacific Oceans, 

 and in this, bound up as it is with the history of Gondwana- 

 land, it may well be that the key to many a geological puzzle 

 will yet be found. 



This second and concluding part of Mr. C. D. Sherborn's 

 Index lo the Genera and Species of the Forctminifera (NoN — Z) 

 has been published by the Smithsonian Institution. It shows 

 signs of the most scrupulous care in preparation, and should 

 prove a boon to future workers on the Foraminifera. 



The Jubilee of the Chemical Society of London was cele- 

 brated in 1891, and it forined the subject of articles in these 

 columns at the time. A record of the proceedings, together 

 with an account of the history and development of the Society, 

 has now been published in a souvenir volume. Translations are 

 given of the addresses sent by foreign societies, and of the speeches 

 made by the foreign delegates. A translation is also given of 

 M. Dumas' Faraday lecture, as well as abstracts of the five other 

 Faraday lectures. The Society boasts of being the first which 

 was formed solely for the study of chemistry, and success has 

 attended it from its foundation. It soon became a centre of the 

 chemical life of this country, and by its publications it has played 

 the chief part in the advancement of chemistry. The volume 



