238 On the Measure of 
From thése results’ it ‘appears, that when 
the contracted vein is not opaque, ‘and when’ ' 
its -vélocity is nearly equal to that whichis due |» 
tothe head, the reaction is'nearly equal to’ 
what it was concluded to be by Sir Isaac 
Newton and M.D. Bernoulli ; and the great 
apparent difference between Sir Isaac Newton’s ~ 
first and second conclusions arises from his 
haviig been misled by some experiments to 
which he alludes: He says—“ Per experi- | 
menta vero constat, quod’ quantitas aque, | 
que, per foramen circulare in fundo vasis 
factum, dato tempore effluit, ea sit, que cum — 
velocitate preedicta,” [viz. the velocity due to 
the head] “non per foramen illud, sed per 
foramen circulare, cujus diametrum est ad 
diametrum foraminis illius ut 21 ad 25, 
eodem tempore effluere debet.”* We 
must presume, however, that he refers to ex- 
periments made by others ; for if he had made 
them himself, he would, no doubt, have arrived 
at. the same results which have since been so 
well established by various authors, and he 
would have stated the above ratio to be as 
19.5 to 25 nearly. 
But his demonstration of the reaction re- 
quires that the velocity at the contracted vein 
shall be equal to that which is due to the head. 
* Principia, edit. 2. lib. 2. prop. 36. 
