other, at the corner of the pipe where they firff met, 
and alfo at the oppofite corner. And, as it is a 
known principle of mechanics, that a body, which 
is aCted upon by two forces moving in different di- 
rections, will defcribe the diagonal of a parallelo- 
gram, of which the directions of thofe forces fhall 
be the tides j fo here, the line in which the two 
ffreams met, and impeded each other’s motion, has 
plainly, as the marble increafed, gone on in the 
diagonal of fuch a parallelogram from both the cor- 
ners i viz. from that where the pipe joined the 
fhoots, or troughs, and from the oppofite one : but 
it is alfo very remarkable, that there is fuch a dia- 
gonal line, not only at thefe corners, but in like 
manner at the other two ; which can be accounted 
for no otherwife, than by fuppofing that each of the 
two ffreams, dafhing againff the oppofite fide of the 
pipe, formed continually, the whole way down, an- 
other ffream, in a contrary direction, as reprefented 
in Fig. 3 ; and fo, both together, produced the fame 
effeCt throughout the whole pipe, as if there had 
been four ffreams flowing over the four hides. Upon 
examining the block, however, very ftriCtly, it ap- 
pears, that the lines in the diagonal one way, are 
ffronger than thofe in the diagonal the other way ; 
and indeed the fpccimen of the pipe, prefented to the 
Society, has even broken in halves, exaCtly in one 
of the diagonals, though the block here defcribed 
remains intire, and has the appearance of having 
had its fides joined accurately, in the manner in 
which a fkilful workman would fit four hoards to. 
be elued together. 
