Sample containing 25% of nickel no appreciable change was detected; others containing larger percentages, and tested in fields up to 2000, all exhibited elongation, which tended to an **asymptotic** value as the field was increased.

The origin of co-ordinates 0 corresponds to v = 0; and the **asymptotic** points J, J', round which the curve revolves in an ever-closing spiral, correspond to v= =co .

X The involute of the catenary is called the tractory, tractrix or antifriction curve; it has a cusp at the vertex of the catenary, and is **asymptotic** to the directrix.

The curve is symmetrical about the line x = y, and consists of two infinite branches **asymptotic** to the line x+y+a = o and a loop in the first quadrant.

The curve is symmetrical about the axis of x, and consists of two infinite branches **asymptotic** to the line BT and forming a cusp at the origin.