The modulus or coefficient of the elasticity of any substance is the measure of its elastic reaction or force, and is the height of a column of the same substance, capable of producing a pressure on its base, which is to the weight causing a certain degree of compression, as the length of the substance to the diminution of its length.

It is computed by this analogy: As the extension or diminution of the length of any given substance is to its lenght in inches, so is the force that produced that extension or diminution to the modulus of its elasticity.

Or, x: P:: l:w = -, x representing the length a substance 1 in square x and 1 foot in length would be extended or diminished by the force P, and w the weight of the modulus in lbs.

*The experments of Mr. Hodgkinson on iron of low tensile strength gives a mean of 6.595 to l.

The results, us given by Mr. Telford, included experiments upon Swedish iron; hence they are omitted in this summary.