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. 



