[ 3i° ] 
We mull Aril beg leave to make an eafy poflula- 
tum, viz. that the nerves are the immediate inftru- 
ments of fenfation, though they are differently or- 
ganized for the different fenfes* 
Obfervations , proving that the fenjatiom of which we 
take cogn'vzance are merely relative. 
It is a certain fadt, that, in the fever al fenfes, the 
proper objedts being luppofe prefent, the fenfarion is 
intirely relative ; or, in other words, that the prefence 
of a powerful objedt always obliterates the prefent 
fenfation of a weak objedt ; and that the conftant ha- 
bitual prefence of any one objedt, in the lame given 
degree, produces no fenfation at all. 
Thus we obferve, that the light of the fun extin- 
guifhes the light of the liars a ltronger tafte covers a 
weaker ; the found of a drum drowns an ordinary 
human voice ; itching is banilhed by fmart and pain ; 
a weak lcent, by one that is Arong ; cold, or a lefs 
degree of warmth, by heat, or a greater degree of 
warmth; and univerfally, our daily experience de- 
monftrates to us, that every organ of fenfe, made 
familiar to a given degree of its objedt, affords no 
manner of fenfation of the objedt in the given degree. 
Thus it fares with the warm blood, which lias 
conftantly flowed through the whole minute fub- 
ftance ofeverymufcleof voluntary motion in an animal 
body, from the time of their formation, or unfold- 
ing in the womb. And it is highly probable, that 
the quickening of the child in a woman is no other 
than the completion of that Hate, in which the blood 
begins freely to flow through, and to afledt the in- 
ftruments of voluntary motion 5 and till it becomes 
familiar 
