19. As shown in the figure, in the triangular pyramid P–ABC, $\mathrm { PA } \perp$ plane $\mathrm { ABC } , PA = 1 , AB = 1 , AC = 2 , \angle B A C = 60 ^ { \circ }$.\\
(1) Find the volume of the triangular pyramid P–ABC;\\
(2) Prove: There exists a point M on the line segment PC such that $\mathrm { AC } \perp \mathrm { BM }$, and find the value of $\frac { P M } { M C }$.\\
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