182 Prof. Nepomuk Fuchs' Chemical Views regarding 



with three readers be used nine times, first by the method of 

 single observation and then by that of repetition. The first 

 method would require 108 readings, and would give a probable 



inaccuracy of —~r= • The second would need only 12 readings, 



and would give an inaccuracy of ■ /— , that is, with one-ninth 



of the labour in reading, just three times the degree of exacti- 

 tude. So much for the error of graduation. As for that of 

 fixing, the clamp is more frequently needed in the operation of 

 frequent single readings than in that of repetition ; and thus 

 the latter has here also the decided advantage. In neither case 

 can the precision go beyond what the telescope is capable of 

 exhibiting. 



We must not, on this account, suppose that the relative merits 

 of a French repeating theodolite and an English single one are 

 settled ; but this I think is quite determined by the investiga- 

 tion that the same instrument is capable of giving much better 

 results by the method of repetition than by that of single ob- 

 servation. 



Chemical Views regarding the Formation ofRochs, which seem 

 to afford new arguments injavour of' Neptunism. By Pro- 

 fessor and Mining Director Nepomuk Fuchs of Munich.'; 



It is now admitted that Werner ascribed by much too great 

 an influence to the agency of water. The minerals of which 

 the greatest mountain masses are composed, are either insoluble 

 in water, or soluble in so slight a degree, that in order to dis- 

 solve them, a much larger mass of water would be requisite 

 than at present exists on the earth. Were we to assume that 

 every thing ha i been dissolved in water, it could hardly be pos- 

 sible to explain how the compound mountain-rocks, such as 

 granite, could have resulted from aqueous solution by means of 

 gradual crystallization. As the different minerals contained in 

 the mixture possess different degrees of solubility, and of the 

 power of crystallizing, they should not necessarily have been de- 

 posited in strata, and they could not, under certain relations, have 



