of a metallic Substance called Palladium. 317 
as the disposing cause that nitric acid is decomposed by those 
metals. But it is evident that some other action takes place ; 
for, sulphuric acid, which has a stronger affinity for oxide of 
platina than muriatic acid, does not in the least promote the 
decomposition of nitric acid by gold, or by platina. 
CONCLUSION. 
The substance which has been treated of in this Paper, must 
convince us how dangerous it is to form a theory before we are 
provided with a sufficient number of facts, or to substitute the 
results of a few observations, for the general laws of nature. If 
a theory is sometimes useful, as a standard to which we may 
refer our knowledge, it is at other times prejudicial, by creating 
an attachment in our minds to preconceived ideas, which have 
been admitted without inquiring whether from truth or from 
convenience. We easily correct our judgment as to facts; and 
the evidence of experiment is equally convincing to all persons. 
But theories, not admitting of mathematical demonstration, and 
being but the interpretation of a series of facts, are the creatures 
of opinion, and are governed by the various impressions made 
upon every individual. Nature laughs at our speculations ; and 
though from time to time we receive such warnings as should 
awaken us to a due sense of our limited knowledge, we are 
presented with an ample compensation, in the extension of our 
views, and a nearer approach to immutable truth. 
The affinities of metals for each other are likely to be of the 
most extensive influence in chemistry. They will promote scep- 
ticism with regard to future discoveries, and throw some doubts 
upon our present knowledge. Palladium is certainly not less 
different from the elements that compose it, and from all other 
MDCCCIII. T t 
