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6 g. There is another reafon why this different 
organization of the different parts of the elephant’s 
tooth makes it neceffary to determine exadly the 
parts that are to be made ufe of in hygrometers. 
Without this precaution it might happen that the 
pipes, which ought to be ffmilar in every refpeCl, 
might be made of fubftances that really differed in 
their dilatability and fenfibility ; that is, of fubftances 
which the humor might affeCt more or lefs ftrongly, 
or more or lefs quickly. This confideration will per- 
haps oblige us to determine both the fize of the 
tooth, and the diftance at which the piece ought to 
be cut off from its apex : for the organization may 
with equal probability vary in teeth of different 
thicknefs, and from the apex to the bafe ; as it does 
in the breadth of the fame tooth. I was not fuf- 
iiciently certain of the fuccefs of my inftrument, to 
take all thefe precautions when I firft fet about it, 
but at prefent I believe them to be important. 
70. There is ft ill another precaution, which in- 
deed I thought neceffary from the beginning, but 
which I could not manage as I wifhed for want of 
proper tools; that is, to perforate the ivory^pipe 
exactly in the direction of its fibres. For let the 
channel have ever fo fmall a degree of obliquity with 
refpeCt to this direction of the fibres, thefe fibres 
will neceffarily be cut in different places; which 
weakening the pipe where it happens, neither its di- 
latations nor its contractions can of courfe be regu- 
lar. 
71. I own here are a great number of precau- 
tions ; but they will not furprize true philofophers. 
They are accuftomed to obferve the operations of 
Vol. LXill. L 1 1 nature 
