ar, and laid in place when hot. It was then packed together by being
tamped and rolled, and a thin covering of the tarred sand placed upon
the top, forming a smooth, hard surface. The first floor consisted of
two inches of matched spruce, grooved on both sides, and fitted with
hard pine splines, five-eighths by one and one-fourth inches. On the
top of this a hard pine 11/4 inch floor was laid over a course of
building paper.

Another method, which is certainly more novel than either of the
others, consists in supporting a floor upon a bed of resin. The
underlying earth was removed, and replaced with spent moulding sand,
leaving trenches for the floor timbers, which were placed upon bricks
laid without mortar. Melted resin was poured into the space alongside
and underneath the timbers. The floor planks were then laid upon the
timbers, the tops of which were about half an inch above the level of
the sand. Holes were bored into the floor plank about four feet apart,
and melted resin then poured into the holes, so as to interpose a
layer of resin underneath the floor plank and beams. Upon this floor a
top floor of hard wood was laid in the usual manner. This floor has
been used for a number of years to support a large quantity of heavy
machine tools, principally planers, without yielding or depreciation
due to decay, and has proved to be most satisfactory.

In some instances asphaltum or coal tar concrete floors are not
covered with wood, although it is much more agreeable for the help to
stand upon wooden floors. It should be remembered that all these
compounds are readily softened by means of oil, and they should be
protected from oil by a coat of paint when not covered with wood; the
preferable method being to first apply a priming containing very
little oil, or a coat of shellac, and follow with some paint mixed up
with boiled linseed oil.

(_To be continued._)

* * * * *

THE MECHANICAL EQUIVALENT OF HEAT.

BY DE VOLSON WOOD, PROFESSOR OF ENGINEERING IN STEVENS INSTITUTE OF
TECHNOLOGY.

It is clearly intimated by Mr. Hanssen, in his determination of the
mechanical equivalent of heat, published in the Scientific American
Supplement, No. 642, April 21, 1888, that his object is to determine
the _absolute_ value of this constant. With his data he finds it to be
771.89 foot pounds. But the determination by direct experiment gives a
larger value. Thus, the most reliable experim