New Doctrines on Mathematical and other Certainty. 13i 
would lead one to believe that granite occurred on Skiddaw it- 
self. This is not the case: the nearest occurrence of granite to 
Skiddaw is at a considerable distance on the east of the moun- 
tain, beyond where granite again occurs, on the road between - 
Kendal and Chale. There is a third station in that district of 
country where granite is also found; on the sea coast, near 
Muncaster; besides which in Wartdale, as well as at Buttermere, 
@ species of rock occurs, which bears a strong resemblance to 
some varieties of granite. I found the relations of these two 
jast-mentioned rocks so very obscurely marked, that I cannot 
pretend to give any opinion about them. I notice the localities, 
with a view to direct the: attention of other geologists. My 
visits to this beautiful country have been pretty much like those 
of other tourists ; 1 have therefore had little time to follow up 
any observations.—I have seldom found any country so very 
puzzling to make out, or to describe geologically in any thing 
like a satisfactory manner. To this, therefore, I attribute the 
neglect it appears to have experienced. It remains a fertile 
source of geological disquisition, and theorists will find it as dif- 
ficult to accommoiate to their respective opinions as any district 
between this and Kamschatka. 
Yours, 
Edinburgh, Feb. 15, 1816. S.N. 
¢ 
XXIX. New Doctrines, as to the Nature of Mathematical and 
other Certainty. 
To Mr. Tilloch. 
Sir, — Hoavrenme a few evenings ago to be in a company 
of persons supposed to be distinguished by their learning and 
acquirements, the subject of conversation accidentally turned on 
the nature of the evidences of different truths or certainties; when 
the Editor of one of our Monthly Journals being present, he 
with great earnestness maintained, that there is no kind of su- 
periority in mathematical certainty over that arising from testi- 
mony; ‘ and mathematicians (said he) have deceived themselves 
into a contrary belief, from not heing aware that every {wo 
things, said by them to be demonstrated to be equa/, are in 
reality the same thing !. When for instance (continued he) they 
say, the three angles of a triangle are equal to two right ones, 
their reasoning only amounts to showing that they are the same!” 
and so on. 
One of the company happening now to remark, that this was 
but to over-look the distinction between and to confound ie 
12 ity 
