432 Magnus on the Condensation of Vapours. 



Whole amount of water in a vertical column of the atmo- 

 sphere, 5*6 inches. 



Thunder was heard all the afternoon, and a thunderstorm 

 occurred on the afternoon of the 20th. 



On the evening of the 29th the earthquake pendulum 

 showed a sensible movement of the earth from WW. to ESE., 

 and that from this time till noon on the 30th the earth was in 

 constant gentle movement. 



Rain only fell on nine days in May, the amount being only 

 1\ inches, the barometer ranging between 29*7 and 30*2 

 inches. 



From the 13th to the 20th there was scarcely any ozone, 

 and during this period an almost cloudless sky. 



MAGNUS ON THE CONDENSATION OF VAPOUES: 



The Archives des Sciences, No. 77, and Poggendorf s Annalen, 

 cxxi., p. 1 74, contain an account of some important researches of 

 M. Magnus on the condensation of vapours on the surface of 

 solid bodies, from which we extract the leading facts : — 



M. Magnus begins by referring to a former paper, in 

 which he showed that a thermo-electric pile grows warmer 

 when moist air is brought into contact with its surface, and 

 grows cooler under a similar contact with dry air. These 

 effect s are produced whether the surface of the instrument is 

 blackened with smoke, or is kept bright. He considered that 

 i lie elevation of temperature was due to the latent heat 

 evolved by the vapour during condensation. Pursuing the 

 investigation in a manner that is detailed in the publications to 

 which we hope referred, the conclusion was arrived at that all 

 Substances grew warmer wlien brought into contact- with air 



more moist than thai which surrounds them, and became 



cooler iii contact with air t hat is more dry. 1 n order, however, 



to enable this action to become sensible, the plates must not 

 he boo thick-, 'flu degree of disturbance varies with the 

 nature of the plates employed, with the dimensions of their 



SUrfaceSj and with t heir I bickneSS ; hut the effects are universal, 

 whether the surfaces he rough or smooth. In employing glass 

 the strongest effect was noticed when tin; plates were very 

 thin, such as are \\<vA for microscopic objects or for polarizing 

 piles. Experiments were made with brass, glass, gypsum, 

 mica, s:il gemmi, and alum. When ungreased leather, wood, 

 ivory, L'-utta pereha, and certain other substances were 



