The vanishing of this invariant is the condition for equal roots.
Locks (East London Advertiser, 1902); Philip Norman, London vanished and vanishing (1905); Records of the London Topographical Society; Monographs of the Committee for the Survey of the Memorials of Greater London.
We find that if the series of excitations of the muscle be prolonged beyond the short stage of initial improvement, the contractions, after being well maintained for a time, later decline in force and speed, and ultimately dwindle even to vanishing point.
This implies the vanishing of the discriminant of the original form.
The discriminant, whose vanishing is the condition that f may possess two equal roots, has the expression j 2 - 6 i 3; it is nine times the discriminant of the cubic resolvent k 3 - 2 ik- 3j, and has also the expression 4(1, t') 6 .