C *97 ] 
being well acquainted with the fpecific difference of 
each plant, before it ripens its feed, it is not a little 
difficult to diftinguifh them one from the other. 
This fpecific difference will be beft furnifhed by the 
leaves. Thus in the henbane, the leaves of the white 
are placed upon long footftaiks ; thofe of the black 
have none, but the lower extremity of the leaf fur- 
rounds the flalk. 
XXIX. Tie beft Proportions for Steam-Engine 
Cylinders, of a give?z Cozitent, confiderd \ 
by Francis Blake, Efq\ F. R . S* 
Read May z 3 HE fire-engine, or (to term it more 
I751 ‘ properly) the ffeam-engine, for 
draining of mines, is a mafter-piece of machinery, a 
very capital contrivance in the works of art, and me- 
riting our attention for further improvements. This 
is univerfally allowed, as well upon account of the 
theory it is founded on, as its ufefulnefs in practice. 
And is it arriv'd then at the laft degree of perfection, 
that we appear at a ffand ? I think not. The pro- 
digious veffel of water to be kept always boiling, 
when only an inconfiderable part of it is employ’d in 
the work, favours too little of the frugality of nature, 
which we ought ever to imitate. But waving that 
now, what I would inquire into here, and endea- 
vour to regulate, is, the cylinder’s proportion of the 
altitude and bafe $ which hath not, as I know of, 
been hitherto noticed. 
T«. 
it 
