.0000000

The method of obtaining the decimals representing the acceleration for
1 deg., at any point, was fully explained in the paper, and compared with
the similar method of showing the uniform acceleration of a body acted
on by a constant force. The ordinary tables in the hand-books, going
only to five places of decimals, are of no use for these computations.

I would suggest a practical experiment. Let any one having an engine
running at a good speed, loosen the crank pin brasses a little, so
that, at starting, it will thump heavily. Let the engine be lightly
loaded, so that only a small portion of the boiler pressure will need
to be admitted to the cylinder. As its speed increases, the thump
will die away; and, if at its full speed, the pressure of the steam
admitted is not so great as to overcome the centrifugal strain of the
reciprocating parts on the crank, as it passes the centers, the engine
will revolve in silence. Any one can ascertain, by the rule given
in the note to the paper, just what pressure can be admitted without
causing a thump, or this can be found by a little experimenting. I am
running an engine which does not thump with loose crank pin brasses,
under eighty pounds pressure, admitted sharply on the centers.

Charles T. Porter.

* * * * *

ANSWER TO PRACTICAL PROBLEM.

MESSRS. EDITORS;--I submit the following solution of "Practical
Problem" on page 147:

Given AB, arm, C, arm, D, chord of half angle of oscillation of arm,
D, and angles of arms, with line AB.

To find angles, BAc', ABb, and length of link, E.

1. As the length of arm, D, is to the chord of arc, ab, divided by
2, so is the radius to the sine angle oscillation of arm, D, divided
by 4.

2. 360 deg. is to the whole circumference as the angle bBa is to the
length of arc ab.

3. Now arc ab is equal to arc a'c'.

4. The whole circumference is to 360 deg. as the length of arc a'e' is
to the angle oscillation of C divided by 2.

5. Half angle oscillation, C, taken from angle BAa' is equal to angle
BAc'.

6. Half angle oscillation, D, taken from angle ABa is equal to angle
ABb.

7. The diagonal of the rectangle formed by the (sum of the sines of
the angles of the arms with AB) into (AB--sum of cosines of same) will
be the length of link, E.

[Illustration]

G. R. NASH, Civil Engineer.

North Adams, Mass.

[We have received other solutions of this problem, but as this covers
the