e is a brake on one of the roughed wheels to check or stop the
motion of the integraph when required.

The instrument works best when the chariots, A and B, are about
opposite to each other; when they are at opposite extremities of f f
and f' f' respectively, the pull at P tends to produce a skewing
couple. If the chariot, B, could be put upon f f and work, if needful,
by a double parallelogram from m m, we should have, excepting the skew
pull, some great practical advantages. We might throw the whole of the
weight of the machine on the one pair of friction wheels, and replace
the other pair by a single wheel, the portion q' f' f' q' of the
machine virtually disappearing. Three wheels, of course, would be a
real improvement. Further, we should have the sum curve and primitive
drawn to the same base line, and the simplification in the number of
parts ought largely to reduce the cost of the instrument.

To be able to perform "inverse summation" (which in the language of
differential calculus is to find y as a function of x, when we are
given y=f(dy/dx), and not dy/dx=f(x) as usual), we only want a means
of making the plane of the wheel, w, parallel instead of perpendicular
to m' m', and it is easy to design a modification in the construction
which will allow of this change.

I hope the above description of the integraph may have made its
construction and method of working sufficiently clear. Those of you
who have a taste for mechanical work, and the necessary tools, might,
I think, with some patience, construct a workable integraph. I expect
the pivots would be the hardest part of the work. I hope, some day,
myself to have another instrument made with a more readily changeable
polar distance, with trace and guide points working in the same
vertical, and a wheel permitting of inverse summation. If this project
is ever carried out, I hope I may be permitted to communicate further
particulars to our society.

* * * * *

After some forty years of immersion in the waters of the pool of
Echoschacht, not far from Hermannstadt, several human bodies have been
brought to the surface in a state of perfect preservation.

* * * * *

SOME HINTS ON SPIKING TRACK.

The usual dimensions of track spikes are 51/2 X 9.16 inches square,
their weight about half a pound each. Their common defects are
brittleness and imperfect points. In spiking track, the most impo