February 23, 1883.1 



SCIENCE. 



67 



ture were found in both the lymphatic glands and 

 the bone-marrow. 



The blood of a dog which has undergone splenot- 

 omy, when transfused into the vessels of another 

 dog, causes in the lymph-glands and bone-marrow 

 phenomena similar to those above described. The 

 author thinks they are in the main due to increased 

 extravasation (? diapedesis) of red blood corpuscles. 

 H. Newell Mahtin. 



THE CACHAR EARTHQUAKE OF 1869. 



The Geological survey of India publishes in vol. 

 xix., part i., of its memoirs (1882), an account and 

 discussion of the Cachar earthquake of north-eastern 

 India, Jan. 10, 1869. The observations were made 

 and the study begun by the late Dr. Thomas Oldham, 

 then superintendent of the Survey: the work is lately 

 completed by his son, R. D. Oldham, now a member 

 of the geological corps The memoir gives a general 

 account of the shock and its destructive effects; 

 notices of previous descriptions by Oldham, sen., 

 Godwin-Austen, H. F. Blanford, and Archdeacon 

 Pratt, which in the present view seem largely erro- 

 neous in their theoretical jiarts ; and a discussion of 

 the position, depth, and shape of the seismic area, 

 and the velocity of the earth-wave's motion and 

 translation. It is well illustrated by photographs, 

 lithographs, diagrams, and maps. 



Cachar (or Silchar), where the shock produced 

 great destruction, and after which it was named, is a 

 town on the Barak river, at the southern base of the 

 rainy Jaintia hills, about 300 miles north-east of Cal- 

 cutta. The seismic vertical was some 80 miles far- 

 ther north, as determined by thirty-six intersections 

 falling witiiin an area forty miles by four or five; or, 

 excluding the less satisfactory lines, on an area • 

 twenty miles by three or four. The depth of the 

 focus is estimated from several tolerably accurate ob- 

 servations at two stations, at thirty miles — or some- 

 where between twenty-five and tliirty-five miles — 

 below the surface. The area over which the shock 

 was felt was an oval measuring 650 miles north-east 

 and south-west, and 400 miles across, covering 250,000 

 square miles, and including Patna and Hazaribagli on 

 the west; the Ganges delta and Chittagong on the 

 south; the head waters of the Namtonai (branch of 

 Irrawaddy) on the east; and the southern slope of 

 the Himalaya on the north. In the latter direction, 

 the extension of the shock was not determined. 

 Within this, a smaller oval or isoseismal line is drawn 

 to show the region of great destruction ; this is sym- 

 metrically placed around the seismic centre. The 

 velocity of wave-translations, estimated over a dif- 

 ference of seismic radii of 180 miles, ^ was 1.2 miles 

 a second, which is regarded as very high and improb- 

 able, although the observations on which it is based 

 — clironometer time noted by Major Godwin- Austen 

 in the hills forty miles north-east of Cachar, and 

 the clocks stopped by the shock in the surveyor- 

 general's oiHce in Calcutta — seem trustworthy. The 

 wave-motion, even at a distance of eighty-five miles 

 from the seismic vertical, was thirty feet a second ; 

 decidedly greater than that found by Mallet for the 

 Neapolitan earthquake of 1857. The large value of 

 the angle of emergence at Cachar is ingeniously 

 accounted for as a result of maward refraction of the 



1 There seems to be an error of 100 miles in the disUnce of 

 Calcutta from the seismic vertical given on p. 84. Correcling 

 this, there would be a difference of 280 miles between the two 

 seismic radii in question, and the velocity of wave-translation 

 would rise to about two miles a second, — even more excessive 

 than is given in the text. 



wave in passing through the loose alluvial sands. 

 In spite of the violence of the shock, few lives were 

 lost, and few buildings overthrown: the reason being 

 that most of the liouses are of. wood and bamboo, 

 elastic enough to escape great injury; or, if of ma- 

 sonry or brickwork, the walls are heavy and low, 

 supporting each other against overtlirow. A church- 

 tower, a saw-mill, and a two-storied palace were 

 thrown down. A secondary action of the shock pro- 

 duced greater destruction at certain points. The 

 alluvial deposits along the river-bottoms sometimes 

 contain strata of soft, water-logged quicksand ; and 

 where the heavy clays overlying these are cut through 

 by the streams, they are often cracked parallel to the 

 steep bank by the earth-wave, and then settle down, 

 and slide on the soft sands beneath. If this happen 

 in a village, the buildings are torn to pieces by the 

 differential motion of their foimdations, even if able 

 to escape- the effect of the shock. Connected with 

 this effect is the formation of ' sand-craters,' which 

 are shown to result from the wet quicksand being 

 forced up through a vent or crevice opened in the 

 overlying clays; the open cup-like form being pro- 

 duced by the back-flow of the water after the shock 

 passes on. These are finely illustrated, and at once 

 recall the figures given in Lyell's ' Principles ' of the 

 ' circular hollows ' formed on the Calabrian plains 

 by the earthquake of 1783. . 



Tlie memoir closes with an appendix giving simple 

 instructions for earthquake observations, and we 

 cordially join the author in the hope that such obser- 

 vations may soon be undertaken at the meteorologi- 

 cal stations throughout the earthquake districts of 

 India. W. M. Davis. 



LETTERS TO THE EDITOR. 



[ Correspondents are requested to be as brief as possible. The 

 writer's name is hi all cases required as proof of good faiih.^ 



A class-room experiment. 



The class experiment commonly employed for 

 demonstrating chemical decomposition consists in 

 heating mercuric oxide, and showing that oxygen is 

 given off wliile mercury remains behind. An easier 

 and equally beautiful experiment may be performed 

 with crystallized copper formate. This salt, when 

 heated over a gas-flame in a dry test-tube, readily 

 decomposes; oxides of carbon are evolved, and a 

 brilliant residue of metallic copper is left. The for- 

 mate is easily ]3repared by boiling copper oxide with 

 formic acid, and filtering. On cooling, fine blue 

 crystals are deposited. -Although this experiment 

 involves no new facts, I believe its applicability to 

 class-room purposes has been generally overlooked. 

 F. W. Clahke. 



Domestic ducks that fly abroad like pigeons. 



Facts relating to the history of the domestication 

 of animals are so rare that it is highly important to 

 keep them in view when once tliey are presented. In 

 this category may be placed O'Donovan's account of 

 the domestic ducks of the Caspian Turcomans. He 

 noticed, especially in the villages bordering upon the 

 south-eastern coast of the Caspian Sea and the Atte- 

 rex delta, that great flocks of ducks are reared by the 

 inhabitants. 



" But so nomadic are the habits of these birds, and so strong 

 are they upon the wing, that it is all but impossible to distin- 

 guish them from their wilder brethren that people these soli- 

 tudes in such vast numbers. I have frequently been astonished 

 at seeing what I took to be a crowd of fifty or sixty mallards 

 come flying into tiic midst of the village, and, forming in some 

 open space, proceed to march in serried files into the hut devoted 



