The description of a new, easy, and accurate method of adjusting the back observation glass : of Wright's improved patent octant, and the method of using it in taking the apparent altitude of the sun at sea and measuring angular distance from 0 to 180 [deWright, Gabriel, mathematical instrument makerca. 1785]"Made and sold by Gregory and Wright (the patentees), mathematical instrument makers near the India House, Leadenhail Street"--p. 4."Suppose ... the following observation were taken June 10, 1785"--P. 2.Folded plate (20 x 30 cm.) loose, originally tipped in between p. 2-3.mixed materialtext