Mechanical Science* wo 



effect of the pressure is in this case supposed to be that of making 

 the vessel a little thinner. 



M. Oersted, to prove his opinion, compressed water in vessels 

 formed from very different materials, and having very different com- 

 pressibilities in themselves. Thus he compared the results obtained 

 in lead, with those obtained in glass ; the former according to him 

 being 18 times more compressible than the latter. After making 

 the necessary corrections, he found that the apparent compressibility 

 of water in lead was a very little more than in glass — the difference 

 being only two millionths of the whole volume of water under the 

 pressure of one atmosphere. Instead of this result, he states that 

 the water ought to seem to expand, if, as his opponents say, the 

 vessel contracts under the pressure as if it were the exterior of a 

 solid mass of lead. 



Similar results were obtained with bottles of brass and tin, and the 

 details of all the experiments will shortly be published. M. Oersted 

 cautions experimenters against the errors occasioned by bubbles 

 of air, oflen found when water remains long in contact with metals, 

 and also against an apparent effect of great compressibility when 

 water has been for a short time only in contact with the surface of 

 glass or metal. 



In a note, appended to the remarks of M. Oersted, is a mathe- 

 matical investigation of the question by M. Poisson, in which he 

 arrives at the directly contrary result, i. e. the opinion adopted by 

 MM. Colladon and Sturm, and states that a hollow sphere equally 

 pressed within and without, suffers, when all other things are equal, 

 the same diminution in radius as if it were a perfectly solid globe. 

 From the same train of reasoning he also draws the conclusion, 

 that calculating, from the same experiment, on the compression of 

 a bar of lead, as that referred to by M. Oersted, the diminution in 

 capacity of a leaden bottle is only one half of that stated by the 

 latter philosopher in his remarks. — Annates de Chimie, xxxviii. 326. 



3. Maximum Density of Salt Water. — A highly interesting set 

 of experiments upon the maximum density of solutions of common 

 salt has been made by Dr. Erman, fils, the results of which are as 

 follows. 



i. Salt water of specific gravity 1.027 has no maximum, of con- 

 densation whilst it remains Hquid ; even when ice is forming in it, 

 the portion remaining increases in density as the temperature falls. 



ii. Salt water of specific gravity 1.020 has no maximum of con- 

 densation, or at least its maximum is not sensibly distant from 

 X°. 25 R. (34°.S F.) which is the point of congelation. 



iii. Salt Avater of specific gravity 1.01 has a maximum, but very 

 much lower than in pure water, for it is attained at the temperature 

 of 1°. 5 R. (35°.4 F.). 



It appears, therefore, that the addition of common salt makes 

 the point of maximum density of water descend, and, ultimately, 

 quite disappear; or, what appears more probable, puts it, aS it 



