What is "reciprocally proportional"

Reciprocally \Re*cip"ro*cal*ly\ (r[-e]*s[i^]p"r[-o]*kal*l[y^]), adv.

1. In a reciprocal manner; so that each affects the other, and is equally affected by it; interchangeably; mutually.

   These two particles do reciprocally affect each other with the same force.
   --Bentley.

2. (Math.) In the manner of reciprocals.

   Reciprocally proportional (Arith. & Alg.), proportional, as two variable quantities, so that the one shall have a constant ratio to the reciprocal of the other.