234 On the Measure of 
If a jet of water I (fig. 18) issue from the 
side of a vessel.A, with the. velocity. which a 
body would acquire in falling: freely from the 
_ surface B to C, he says the repulsion. of the 
water in the opposite direction to the e jet. will 
be equal to the weight of a column of ‘water, 
of which the base is equal to the section of 
the contracted vein, and. the height, equal: to 
2 BC. det inna 
This question respecting the ‘amount. of 
what has been termed the “reaction of the 
effluent. water,’ derives additional interest 
from the circumstance of its having particu- 
larly engaged the attention of Sir Isaac 
Newton, and from his having given a solution 
of the problem in the first edition of the 
“Principia,” which he materially altered i in the 
succeeding editions. In the first edition (book 
2d, prop. 37) he infers, that the reaction 1s 
equal to the weight of a column of water cof 
which the base is equal to the area of the 
orifice, and the height equal to that of the 
surface of the water above the orifice. In, the 
succeeding editions, the subject i is more fully 
discussed. in the 36th prop. of the second 
book, where he infers (cor. 4.) that, when the 
area of the surface B is indefinitely large 
compared with that of the orifice, the reaction. 
is, what it was afterwards in a different manner 
