Construction Of Tangent To 2 Circles
An illustration showing how to construct a tangent to 2 given circles of different diameters. "Join the centers C and c of the given circles, and extend the line to D; draw the radii AC and ac parallel with one another. Join Aa, and extend the line to D. On CD as a diameter, draw the half circle CeD; on cD as a diameter, draw the half circle cfD; then the crossings e and f are the tangenting points of the circles."
Albert A. Hopkins Scientific America: Handy Book Of Facts And Formulas (New York: Munn & Co., Inc., 1918) 35