42, Mr. king’s Account of a 
lar account of this production in a paper laid before the 
Society in the year 1773 fi) , and therefor^ lhall fay no- 
thing of it here but what immediately relates to the pre- 
fent purpofe. The pipe was forty-two feet in length, 
and the hollow part of it was feven inches and an half 
wide, by four inches and an half ; and this whole cavity 
was fo filled with the incrufted matter (which was hard 
enough to take an exceeding fine polifh, like the moft 
beautiful marble) that at laft there was left a water way,, 
which, nearly uniformly throughout the whole length 
of the pipe, was only about three inches and an half by 
one inch; and thus there was formed, within the firft 
wooden pipe, a fecond pipe of this incruftration, the 
thicknefs of the fides of which was about one inch and 
an half. On cutting a tranfverfe feCtion of this pipe 
there appeared a number of uniform lines, forming al- 
mofi regular fimilar parallelograms, one within another, 
like the coats of an onion, and plainly denoting the gra- 
. dual and regular progrefs of the formation of the whole 
incruftation. But the circumftance moft remarkable, and 
that is more immediately applicable to the prefent pur- 
pofe, is, that where there was, by accident, the point of a 
nail projecting through the fide of the wooden pipe, it fo 
accelerated the progrefs of the incruftation, that, adjoin- 
ing thereto, the fimilar fides of the firft and outward 
(d) Phil. Tranf. yol, LX11I, p. 241. 
6 paral- 
