My dear Sir,
You will find the subject of Reciprocal polars very well treated of in [illegible] which I now send.
The word reciprocal is sometimes (improperly) used for a curve to a radius vector the reciprocal of another e.g.
[illustration]
if rcosč = a be the equation to a st. line 1/r cosč = a is the equation to a circle 
of which the radius is ½a.
I am Yours vy truly
Philip Kelland
H. F. Talbot Esq