signal rockets. As in the case of the latter, a space is left in the axis
of the cartridges. These rockets are fired from a trough placed at an
inclination of fifty or sixty degrees. Those of three inches illuminate the
earth for a distance of 900 yards. They may be used to advantage in the
operation of signaling.

A _parachute fire_ is a device designed to be ejected from a pot at the end
of the rocket's travel, and to emit a bright light during its slow descent.
It consists of a small cylindrical cardboard box (Fig. 16) filled with
common star paste or Lamarre stars, and attached to a parachute, _e_, by
means of a small brass chain, _d_.

To make this parachute, we cut a circle ten feet in diameter out of a piece
of calico, and divide its circumference into ten or twelve equal parts. At
each point of division we attach a piece of fine hempen cord about three
feet in length, and connect these cords with each other, as well as with
the suspension chain, by ligatures that are protected against the fire by
means of balls of sized paper.

In rockets designed to receive these parachutes, a small cavity is reserved
at the extremity of the cartridge for the reception of 225 grains of
powder. To fill the pot, the chain, _d_, is rolled spirally around the box,
_c_, and the latter is covered with the parachute, _e_, which has been
folded in plaits, and then folded lengthwise alternately in one direction
and the other.

The _parachute port-fire_ consists of a cardboard tube of from quarter to
half an inch in diameter, and from four to five inches in length, closed at
one extremity and filled with star paste. This is connected by a brass wire
with a cotton parachute eight inches in diameter. A rocket pot is capable
of holding twenty of these port-fires.

Parachute fires and port-fires are used to advantage in the operation of
signaling.--_La Nature_.

* * * * *

IMPROVEMENT IN LAYING OUT FRAMES OF VESSELS--THE FRAME TRACER.

By GUSTAVE SONNENBURG.

To avoid the long and time-consuming laying out of a boat by ordinates and
abscissas, I have constructed a handy apparatus, by which it is possible
without much trouble to obtain the sections of a vessel graphically and
sufficiently accurate. The description of its construction is given with
reference to the accompanying cut. A is a wooden rod of rectangular
section, to which are adapted two brackets, a_{1} a_{2}, lined with India
rubber