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 ground in a very simple manner, we think it will be sufficient. Those forwarding the solutions not published will accept our thanks and assurances that it is not because they lack merit that they are declined.--EDS. * * * * * RECIPROCATING PARTS OF STEAM ENGINES.