Scientific Intelligence — Hydrology. 373 



really owing to organic matter, and not merely carbonic acid, — that 

 all the water of great towns contains organic matter, — that water 

 purifies itself from organic inatter in various ways, but particularly 

 by convertincr into nitrates, — that water can never stand long with 

 advantage unless on a large scale, and should bo used when collected 

 or as soon as filtered. 



4. On the Dilatation of Ice hy Increase of Temperature. — Three 

 observers have undertaken to solve this problem by independent trials 

 made in the Observatory of Poulkowa. They have found that the 

 linear dilatation of the ice for 80° H. is 



0-0052356 (M. Schumacher sen.). 

 0-0051270 (M. Pohrt). 

 0-0051813 (M. Moritz). 



The probable error in this latter determination does not exceed 

 ±0-0000190. It is a result so much the more important in the 

 science of caloric, since the only estimate hitherto known on the 

 same subject (that of Placide Heinrich) is almost five times more 

 considerable. 



The observations made at Poulkowa shew that the dilatation of 

 the ice is a simple linear function of temperature, and that it is 

 equal foi all possible directions in a block of ice. 



The quantity of atmospheric carbonic acid increases until we reach 

 a height of 3365-8 metres; at that elevation is the limit of a con- 

 stant maximum. Farther, at greater heights, the variations in quan- 

 tity of carbonic acid are less considerable than in lower places. The 

 immediate glacier atmosphere contains less carbonic acid than the 

 neighbourhood. The ascending curj-ents of air have a greater influ- 

 ence in the distribution of carbonic acid than the common winds. 



5. The Buoyancy of the Water of the Dead Sea. — About sunset, 

 we tried whether a horse and a donkey could swim in the sea (the 

 Dead Sea) without turning over. The result was, that, although the 

 animals turned a little on one side, they did not lose their balance. 

 As Mr Stephens tried his experiment earlier in the season, and 

 nearer tlie north end of the sea; his horse could not have turned 

 over from the greater density of the water there than here. His 

 animal may have been weaker, or, at the time, more exhausted than 

 ours. A muscular man floated nearly breast-high, without the least 

 exertion. 



A horse taken into the bay could, with difficulty, keep himself 

 upright. Two fresh hen-eggs floated up one-third of their length. 

 They would have sunk in the water of the Mediterranean or the At- 

 lantic. 



The water of the sea was very buoyant ; with great difficulty I 

 kept my feet down ; and when I laid upon my back, and, drawing 

 up my knees, placed my hands upon tliem, I rolled immediately 

 over. 



