The centres of circles forming a coaxal system are collinear 2.
The collinear centres are the three sets of one external and two internal centres, and the three external centres.
It is readily seen that if the optical system be symmetrical, the origins of the co-ordinate systems collinear with the optical axis Object J Barrel shaped Cushion shaped Distorted image FIG.
In this way he established the famous theorem that the intersections of the three pairs of opposite sides of a hexagon inscribed in a conic are collinear.
Then the strong interacting particles experience additional radiation of soft or collinear partons described by means of the parton shower.