quire double the thickness to
sustain equal pressure. With regard to the pressure endwise, the area
of a cylinder head 14 inches in diameter is 154 inches, and the
strength of the 44 inches of circumference would be sufficient to
sustain 352,000 lbs., which, divided by the area, is 2,275 lbs. per
square inch. If the diameter is 56 inches, the circumference being
172, would sustain a pressure endwise of 555 lbs. per inch. Thus it
will be seen that if the cylinder were even 20 feet in diameter, the
iron would better sustain the pressure on the head that on the
periphery. With regard to the requisite strength of the cylinder's
head, if they are made in a semi-spherical convex form, they will
require no more thickness of plate than the cylinder: but if they
consist of plane disks, the thickness thereof should bear the same
proportion to that of the periphery that the area in square inches
does to three times the circumference. But in general, no other rule
is observed for the thickness of the heads, than to make them
extravagantly heavy, without much regard to theoretic calculation.

* * * * *

BAGLEY'S GOLD PENS.

Do our readers wish to hear any thing more about them? If so, they
have only to inquire of any one of the many thousands of writers who
have used these pens six months or more, and can hear the fact
attested, that these are decidedly the cheapest pens (at $4) that can
be any where found. Mr. Bagley has recently patented a neat, elegant,
and excellent improvement in the pen-holder, which "takes the shine
off" all precedents. Should our readers find a real good article in
this paper, they may know it was written with one of Bagley's pens.
Nuf ced.

* * * * *

THE HUMMING BIRD.

A gentleman who resided some time on one of the West India Islands
informs us that while he was once travelling along the bed of a deep
ravine overhung with thick vines, he was actually startled by the
immense numbers of humming birds which hovered over and about him.
They hovered about him as if actuated by curiosity alone. They were of
various kinds and colors, some of them being nearly as large as
sparrows, while others were but little larger than a bee. Some were of
a dingy green, or a light brown, while others seemed gaudily arrayed
in plumage as brilliant and variegated as the rainbow. They would
approach within arms length of his face, and pausing in