62 Count de Bournon’s Description , &c. 
substance, or collection of substances, for their basis, and are 
combined with the same modifying substance; and that the 
difference between these minerals, arises merely from the dif- 
ferent proportions of their basis, and of their modifying sub- 
stance. The more I study the works of nature, the more I 
become persuaded of the truth of the above remark ; I am also 
convinced, that a want of attention to this circumstance has led 
mineralogists to confound one species with another. 
If to the above cause of error we add that which is occasioned 
by neglecting, in the analysis of these substances, to distinguish 
those parts which (by their chemical combination and mode of 
attraction) determine the particular nature of the substance 
analysed, from those which enter into its formation in conse- 
quence of the heterogeneous attraction of aggregation, we shall 
readily conceive that it is the duty of chemists to correct gra- 
dually the errors they have occasioned in mineralogy. But I 
must repeat that, in order to correct these errors, it is necessary 
to make a number of comparative analyses of the substance 
whose nature they wish to determine. It is also necessary, that 
the specimens they make use of should be very perfect in their 
kind, taken from various districts, and, as much as possible, from 
various matrices. It may perhaps not be improper to add, that 
the interest of science requires, that the mineralogist and the 
chemist should mutually sanction the operations each of them, 
in his respective department, undertakes to perform. 
