Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2- Appendix): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

274 APPENDIX. country, and establish fresh claims to the gratitude of your coun- trymen, is the sincere wish of. Sir, Your obUged and faithful servants, For Dickson, Price, and Co. — W. Hodgson. Natlor, Kendall, and Co. For Laylem, Read, arid Co. — Valentine Smith. SwAYN, Reid, and Co. Lang, Pearce, and Co. Fredk. Huth, Gruning, and Co. For GiBBs, Crawley, and Co. — H. Witt. J. W. Leadlet. For Hegan, Hall, and Co. — J. Farmer. John Mackie. J. Sutherland. For Christopher Briggs. — H. N, Briggs. Templeman and Bergman. Frederick Pfeiffer. No. 44. Description of a Quadrant, the power of which is increased by means of an additional Horizon Glass. Let CAB, in the figure, represent a common quadrant, having the angle A C B equal to forty-five degrees : let C be the index-glass ; C A the zero hne, or the plane of the glass produced ; D the hori- zon-glass, and E the sight-vane. Suppose C and D to be parallel, and that a ray coming from an object H, is reflected from C, along the line C D, and from D along the line D E to the eye. A ray of light from h may be supposed to come from H, if the two, H h, are more than half a mile from the instrument, and the object H vnH be seen directly, as well as by reflection, in the Une D E. The angle D C E being equal to the angle DEC, D C is equal to D E. With the centre D describe the circle C E F. Place a glass at F, similar to that at D, but making an angle with C B, which will reflect a ray passing along C F, in the line F E, to E.