I. MEASUREMENT. 347 



the first is divided into sixths of a degree, the second into whole degrees, 

 which can be read by a simple pointer, but without verniers. The radius of 

 both circles is 40 cm., and the stand is constructed of cast iron. 



1776. Two Quadrants, with double sights, old; property of 

 H. H. Prince Pless, Fiirstenstein. Committee ofBreslau. 



1777. A Quadrant, for the observation of the height of the 

 sun, old ; property of H. H. Prince Pless, Fiirstenstein. 



Committee ofBreslau. 



1777a. Quadrant, by Langlois. Paris Observatory. 



1778. Pillar Sextant, on stand, with artificial horizon. 



John Browning. 



These instruments are intended for use in an observatory, or otherwise on 

 land, for the purpose of obtaining accurate time. 



1779. A small Semicircle, with double sights, for observing 

 the heights of the sun, old; property of H. H. Prince Pless, 

 Fiirstenstein. Committee of Breslau. 



1780. Model of the Greenwich Transit. 



1781. Two 12-inch Astronomical Quadrants, by Bird, 

 employed in the observations of the transit of Venus. 



Royal Society. 



1782. Prismatic Circle, constructed in 1843, from the design 

 of Professor Kaiser. 



H. G. Van de Sande Bakhuyzen, Director of the Observa- 

 tory at Ley den. 



By means of two observations the measurement of the angle can be obtained 

 without any instrumental error, excepting those of division. Angles can be 

 measured from to 170. 



1783. Kaiser's Prismatic Circle, constructed on the same 

 principles as the preceding. The construction of the stand, 

 and of a few details, have been improved in this second model. 



H. G. Van de Sande Bakhuyzen, Director of the Observa- 

 tory at Ley den. 



d. EQUATORIALS. 



1784. An Equatorial Telescope by Abraham Sharp, an 

 eminent mathematician, mechanist, and astronomer, descended 

 from an ancient family at Little Horton, near Bradford in York- 



