10 M. C. Martins on the relative heating, by Solar Radiation, 



minerals considered as compounds of the sulphides of antimony 

 and lead, for the sake of comparison. 



Specific 

 gravity. 



Name. 



Formula. 



Sulphur. 



Antimony. 



Lead. 



5-3 



Zinckenite. 



PbS4- Sb 2 S 3 



21-6 



43-5 



39-4 



5-5 



Jamesonite. 



3PbS+2Sb 2 S 3 



20-2 



36-2 



43-6 



5-4 



Plagionite. 



4PbS+3Sb 2 S 3 



20-6 



38-3 



411 



5-6 



Heteromorphite. 



2PbS4- Sb^S 3 



19-2 



31-0 



49-8 



58 



Boulangerite. 



3PbS+ Sb2S 3 



179 



241 



58-0 



? 



Meneghinite. 



4PbS + Sb2S 3 



16-7 



19-6 



63-7 



6-40 



Geokronite. 



5PbS+ SbsS 3 



16-5 



16-7 



66-8 



6-47 



Do. (Fablun). 



6PbS+ SbsS 3 



14-5 



14*6 



70-9 



Veins of these antimonial galenas are met with almost every- 

 where, cutting through the Silurian strata of South America. 

 They are generally crystallized, or rather more or less crystal- 

 line; and although they can be procured free from apparent 

 mechanical admixture of other minerals, yet it is extremely diffi- 

 cult to determine the mineral species to which they belong 

 merely by an examination of their external and physical charac- 

 ters, and it is most probable that a closer examination will show 

 the presence of at least more than one new mineral species per- 

 taining to this class. 



The specific gravities of these varieties differ considerably, yet 

 not sufficiently to be a decisive criterion as to the species ; eight 

 varieties of what appeared to be antimonial galena from different 

 mines in the department of La Paz, Bolivia, gave respectively 

 the following specific gravities taken at 60° Fahr. : — 



5-25, 5-302, 5-49, 5'49, 6-515, 7'07, 7-20, 7'41; 



and I have no doubt that on further trial many intermediate 

 numbers would be found ; indeed it would seem as if the sul- 

 phides of antimony and lead would combine in any proportion. 



II. On the relative Heating, by Solar Radiation, of the Soil 

 and of the Air, on a Mountain and in a Plain. By M. 

 Charles Marttns*. 



THE sun's rays falling on the top of a mountain ought, 

 theoretically, to be warmer than those which, after traver- 

 sing the lower and denser strata of our atmosphere, reach the 

 adjacent plain, since these strata necessarily absorb a consider- 

 able quantity of the heat of such rays. Observation fully con- 

 firms the prediction of theory in this case. All travellers who 

 have ascended high mountains have been surprised at the great 



* From the Comptes Rendus de VAcad. des Sciences, October 17, 1864. 



