Copyright (c) 1979 Waddingtons

The game is played on the following board (I don't know the setup, so I propose this for now):

MOVE - Each player, on each turn, moves one of his stones into one of the eight possible directions (orthogonal or diagonal). The stone moves in straight line (bouncing on the edges, see below), until it meets another stone. At that moment, its momentum is transferred and the stone hit moves the same distance. 
If the stone hits a row of stones, only the farthest one moves (as in a Newton's Cradle).
If the second ball, before moving all its distance, hits a third ball, its momentum (i.e., the number of cells already moved), is transferred to that stone, and so on...
A move that does not hit no ball is illegal.
BOUNCING - If a stone hits the edge at 90 degrees, it is bounced back to the opposite direction. If a stone hits the edge at 45 degrees, it continues, after a direction change of 90 degrees.
CAPTURE - If a neutral ball stops inside on of the central holes, it is captured and removed from board.
A move that would capture a non neutral ball is illegal.
GOAL - Wins the player that first captures 5 neutral stones. 

Some examples

The red stone moves north and hits the neutral stone with momentum 2 which is transferred to the neutral moving 2 cells on the same direction.

If the green stone moves north, it will bounce back to south, and hits the neutral stone with momentum 2. Then the neutral stone moves 2 cells and stops at a hole, being captured.

Bouncing and capturing

The green stone moves northwest and bounces the top edge. Then, it hits a neutral stone which receives the momentum 3 and moves on the same direction, until it stops on a hole, being captured by Green.

More bounces

The red stone moves 7 cells, and transfers the momentum to the enemies stone. If red were one cell to the north, the move would be invalid, because the green stone would stop at the hole.