46 Count de Bournon’s Description of a 
by the name of girasol, as being either quartz or calcedony. 
But, it will be said, what is then the nature of those substances ? 
To this question. I can only answer, I do not know; and, un- 
fortunately, those substances are not the only ones respecting 
which we are obliged to confess our ignorance. We make, 
however, one step towards the knowledge of the nature of a 
substance, when we discover that it is not what it has hitherto 
been supposed to be. Calcedony and girasol certainly have for 
their base, the same earth that forms the base of quartz ; but 
that earth appears to me to be differently modified in those sub- 
stances ; that is to say, I do not believe that quartz is merely 
an aggregate of pure quartzose earth. In like manner, I do not 
believe that corundum is merely an aggregate of pure argill. 
Perhaps, among the number of interesting discoveries with which 
chemistry is constantly enriching us, we shall one day be enabled 
to place that of a more intimate acquaintance with the nature of 
the above-mentioned substances. 
Besides the attraction which takes place between the similar 
integrant molecules of substances, which I have already men- 
tioned, there exists another, between these similar molecules and 
those which are dissimilar, or of a different nature. In conse- 
quence of this kind of attraction, during the formation of a 
substance by the aggregation of its similar molecules, other 
molecules of a different substance, being situated near them, 
enter into union with them, either by one molecule uniting with 
another, or by a collection of molecules uniting themselves to a 
molecule. To the first of these, I shall give the name of simple 
homogeneous attraction of aggregation ; the other I shall call 
heterogeneous attraction of aggregation ; and, to those extraneous 
molecules which the last mentioned kind of attraction introduces 
