Ftc. 3.Dlarch stele of root of a F stem of young Fern.
It is (f = (ab) 2 a n-2 r7 2 =Hx - =H; unsymbolically bolically it is a numerical multiple of the determinant a2 f a2f (32 f) 2ï¿½ It is also the first transvectant of the differxi ax axa x 2 ential coefficients of the form with regard to the variables, viz.
In general for a form in n variables the Hessian is 3 2 f 3 2 f a2f ax i ax n ax 2 ax " ï¿½ï¿½ ' axn and there is a remarkable theorem which states that if H =o and n=2, 3, or 4 the original form can be exhibited as a form in I, 2, 3 variables respectively.
The constant multiplier is of no especial interest so that we may take as applicable to the image of a line 0 I = z 2 sin e A f 1+cos ` - 271 - Eh).
of the area A, f f xdxdy = o, ffydxdy = 0, (6) R = p hA, (7) xhA = - cos a f f x 2 dA - sin affxydA, fxydA, (8) yhA = - cos a ff xydA - sin ail y 2 dA.