290 M. Humboldt on the Horary 



I have comprised the soda and the lime under .one head in 

 the formula -^ j- S 3 + 3 AS 3 + 5 Aq, though these two substan- 

 ces do not appear to be isomorphous. The form of anhydrite, 

 CaS 2 , is different from that of anhydrous sulphate of soda, 

 N& 2 as described by Haidinger. The crystals of meionite also, 

 and those of nepheline, cannot be reduced to the same fun- 

 damental form, though the chemical composition of the for- 

 mer, according to the analyses of Leopold Gmelin and 

 Stromeyer may be expressed by the formula CS + 3JS, 

 and that of the latter, according to the analysis of Arfved- 

 son, by the formula NS + 3AS. But it is probable, par- 

 ticularly from the analyses of the mesotypes by Fuchs, that 

 soda, containing a certain quantity of water, may be isomor- 

 phous with lime, in the same manner in which ammonia, with 

 two atoms of water, is isomorphous with potash, as has been 

 shown by Mitscherlich. In this case, it would be necessary 

 to add some of the water to the soda, in order to have it iso- 

 morphous with lime, and the number 5, which is not a com- 

 mon one among this kind of formula?, would then be likewise 

 modified. In the meantime, it will be prudent to express 

 the formula as above, because the quantities of oxygen, con- 

 tained in each, soda and lime, taken separately, are in no 

 simple ratio to the oxygen in the other ingredients, though, 

 particularly in the second analysis, the oxygen of the soda, 

 and that of the lime, are very nearly in the ratio of one to six. 



Art. XXI. On the Horary Variations of the Barometer. 



By Baron Alexander de Humboldt. * 



In the year 1682, f M. M. Varin des Hayes, and De Glos, 

 remarked, that, at Goree, the barometer was generally lower 



* This paper is a brief abstract of the elaborate dissertation on this sub- 

 ject, published in the Relation Historique.—Livrais. 5, Folio, p. 270—313. 



+ We must again repeat here what we have said in No. iv. p. 336, 

 that, in 1666, Dr Beale, an Englishman, observed, " that very often, 

 both in winter and summer, the mercury stood higher in the cold morn- 

 ings and evenings than in the warmer mid-day."— Ed. 



