144 Progress of Foreign Science. 



Dr. Brewster has published, in the last number of his Jour- 

 nal, " Observations on the Production of Electricity by Con- 

 tact, by Professor Gmelin of Tiibingen, in which we find seve- 

 ral experiments, made with the aid of Bohnenberger's new 

 electrometer, with two zarabonic piles, that seem adverse to 

 the above results of the English philosopher. Of one expe- 

 riment with magnesia, the Professor says, " This experiment, 

 which was very often repeated, appeared to refute the experi- 

 ments of Sir H. Davy so fully, that they scarcely seemed to re- 

 quire any further refutation." And he concludes as follows : — 

 " The general result of these experiments is therefore this, that 

 the electrical opposition between acids and bases, though so 

 well established by other means, cannot be deduced from the 

 electrical relation between these bodies and metals." 



Most scientific readers, we believe, will hesitate a little be- 

 fore they give up Sir H. Davy's results, obtained by a simple 

 instrument, which, by the way. Professor Gmelin disparages, 

 for others of an anomalous character, inconsistent with them- 

 selves, and with the welt-known indications of voltaic elec- 

 tricity. 



II. Caloric. We promised in our last to give some ac- 

 count of M. Fourier's speculations on the temperature of the 

 earth. According to Mr. Fox, the temperature of metallic 

 veins is generally from one to three centigrade degrees above 

 that of the contiguous rocks. Considering the currents 

 of air which circulate in the galleries of mines, as a con- 

 stant cooling cause, it would appear that the above small 

 diflference of temperature should be the necessary conse- 

 quence of the great conductibility of metals. It appears, 

 also, that, this phenomenon properly studied, might serve to 

 shew that the interior parts of rocks and metallic veins are 

 themselves at still more elevated temperatures, and that it 

 would thus furnish a new objection against the hypothesis ad- 

 vanced by some philosophers, that the high heat observed in 

 mines proceeds from a chemical action of the air on the sub- 

 stances which line the walls of the galleries, and, in particular, 

 the pyrites. These ideas of M. Arago seem confirmed byM. Fou- 

 rier's investigations. 



1. Suppose that a homogeneous solid mass is enclosed be- 

 tween two infinite parallel planes, and that one of these 

 extreme planes, being exposed to the action of a constant 

 source of heat, is maintained at the fixed temperature 5, whilst 

 the opposite plane, which terminates the solid, is in contact with 

 the atmospherical air standing at a fixed temperature a, less 

 than b. If we conceive that the solid has been subjected for a 

 very long time to these unequal but constant actions, of two 

 exterior causes, the surface in contact with the air will take a 



