An introduction to plain trigonometry : with its application to heights and distances. ... By Richard Cockrel. - Cockrel, Richard. (printed and sold by M. Heavisides, for the author; by Messrs. Law and Son; and Mr. D. Taylor, London; Mr. Pine, Bristol; Messrs. Wilson and Spence, York; and Mr. Nicholson, Barnardcastle, 1792)