546 



SCIENCE. 



[Vol. II., No. 37- 



floating grillage has previously been moored over this 

 place, the ball is caught at the point of rising, and 

 the horizontal distance of this point from the pole 

 measured. Hence are known, upon measuring the 

 depth, the two co-ordinales of the point at the surface 

 from the bottom of the jjole. The author proposes 

 to weight the ball until it shall be one-half the lieavi- 

 ness of water. He deduces some equations to prove 

 that the ball rises with a practically uniform velocity, 

 and observes, that for a depth of 30 feet, from which 

 such a ball would rise in about 11 seconds, and a 

 mean velocity of current of i feet per second, the 

 ball would travel horizontally about 44 feet. — {Amer. 

 enrj., Aug. 24.) c. E. G. [292 



CHEMISTRY. 

 (Phynical.) 

 Determination of vapor density. — Br. Paw- 

 lewsky proposes a modification of Dumas' method in 

 which he uses a globe of 20-.30 cubic centimetres vol- 

 ume. After heating, the globe is closed by a rubber 

 cap, which is fitted to a cylindrical tube of glass 

 sealed at one end. . The volume is therefore constant 

 for different determinations, and the observations 

 may be taken in a room of nearly constant tempera- 

 ture. In the formula of Dumas, — 

 _ O.0OI29P.2. F. -Z?,, 

 "' ~ (1 + at) 760 • '■^•' 



■where m is equal to the weight of air, the product 

 0.0012032 .V = K would be constant. The value 

 (1 + of) = JV is constant, and may be obtained from 

 a table. If, then, the constant, K, is divided by 

 7G0, a new constant, D, results, and (I.) becomes 

 _ jr. lip _ D.Bq 



In a determination at any temperature, i'o> and any 



pressure, B'a, if the weight of air in the apparatus is 



represented by n, its weight is shown in the formula 



0.00120.32 V (l + Kf) B'„ 



"= (1 + a 760 ' ("I-) 



in which k represents the coefficient of expansion of 

 the apparatus. If the temperature is constant, and 

 the same apparatus is used in different determina- 

 tions, the product 0.0012932 V {1 + k t'], and the 

 whole denominator, become constant. Eepresenting 

 the denominator by B, and the product 0.0012932 V 



M 

 (1 -I- Kt) by M, the fraction 1? = C is constant, and 



formula (III.) will take the form 

 MB'o 



(II.) 



B 



= C . B'o. 



(IV.) 



The volume of air may therefore be obtained by 

 multiplying the constant, C, by B' reduced to B'ol 

 and when the weight, a, of the vapor, and that of 

 the air, n, uiuler the same conditions, are Icnown, the 

 vapor density may be found by the formula 



I> = 7' 



(V.) 



The apparatus may be heated in a beaker of medium 

 size, coutaiuing>waler,"oil, or paraffine. For a com- 



plete description of the apparatus, reference must bo 

 made to the original arlicle. A series of determi- 

 nations are given, which indicate a high degree of 

 accuracy. — {Jierichte deulsch. chem. yesellacli., \\i. 

 1293. ) c. F. M. [29a 



GEOLOGY. 

 Evidences of modern geological changes in 

 Alaska. — Mr. T. Meehan exhibited a piece of wood 

 taken from a prostrate tree which had been covered 

 with glacial drift on a peninsula of Hood's Bay, 

 Alaska, formed by the junction of Glacier Bay and 

 Lynn Channel. The trunk, which lay under a block 

 of granite estimated to measure 2,214 cubic feet, was 

 quite sound, and exhibited no evidence of great age 

 since it became covered. The shores are strewn' with 

 rocks and stones of various kinds, as usual in cases 

 of glacial deposits. All the surroundings indicated 

 that there had been a sudden subsidence of the land, 

 accompanied by a flow of water with icebergs and 

 huge bowlders, which crushed and tore off the trees. 

 The whole surface was afterwards covered to a great 

 depth with drift. Since that lime, there must have 

 been an elevation of the land bringing the remains of 

 trees to their original surface, but with a deep deposit 

 above them. A study of the existing vegetation 

 might afford an approximation to the time when 

 these events occurred. The living forest indicated 

 clearly that it could not have been, at the farthest, 

 more than a few hundred years since the elevation 

 occurred. The trees in the immediate vicinity, in- 

 deed, were not more than fifty years old; but unless 

 the original parent trees, which furnished the seed for 

 the uplifted land, were near by, it might take some 

 years for the seed to scatter from bearing trees, grow 

 to maturity, again seed, and, in this way, be spread 

 to where we now find them. But, as original forests 

 were evidently not far distant, two or three hundred 

 years ought to cover all the time required. The 

 Indians of the region have a tradition of a terrible 

 flood about seven or eight generations ago, from 

 which only a few of the natives had escaped in a 

 large canoe. The probable identity of the sunken 

 trees with the present species, and the freshness of 

 the wood, indicate no very great date backwards at 

 which the original subsidence occurred. 



In connection with the subject of the comparative- 

 ly recent occurrence of great geological changes, as 

 indicated by botanical evidence, Mr. Meehan referred 

 to an exposure of the remains of a lai'ge forest near 

 the Muir glacier, — one of five huge ice-fields which 

 form the head of Glacier Bay between Lat. .')0° and 

 60°. This glacier is at least two miles wide' at the 

 mouth, and has an average depth of ice, at this spot, 

 of perhaps five hundred feet. At the present time 

 there is not a vestige of arboreal vegetation to be 

 seen in the neighborhood. The river which flows 

 under the glacier rushes out in a mighty torrent a few 

 miles above the mouth, and has cut its way through 

 mountains of drift, the gorge being many hundred 

 feet in width, and the sides from two hundred to 

 five hundred feet high. The torrent, though the bed 

 is now comparatively level, oarries with it an im- 

 mense quantity_of heavy stones, some of which must 



