194 LATITUDE AND LONGITUDE. 



Nay, start not at my careless tread, 

 I dare not crush thy timid head, 

 Remembrancer of days now fled, 



Sweet Daisy. 



No may'st thou fearlessly expand, 

 And blossom on my native land, 

 Disturbed by none save infant hand, 



Sweet Daisy. 

 M. G. 



LATITUDE AND LONGITUDE. 



Concluded from Page 96. 



Altitudes of the sun or moon taken at sea require 

 four corrections, these are for semidiameter, dip, re- 

 fraction and parallax. 



What is understood by the word diameter of the 

 stars in observation is, not the absolute diameter of 

 their globe but, simply, the angle under which we see 

 this diameter ; this angle diminishes in proportion as 

 the distance increases, and in the same ratio when the 

 distance is small. 



Suppose AB the real diameter of an object, and the 

 angles ACB, ADB were the angles under which we 

 perceived such an object at the points C and D, that 

 is to say the apparent diameters ; now in the right 

 angled triangle ACB we have by trigonometry sine 

 ACB : R : : AB : AC, and in the right angled trian- 

 gle ABD, R : sine ADB : : AD : AC ; therefore, 

 sine ACB : sine ADB : : AD : AC. 



B 



But when the angles are very small the sines arr 

 very nearly in the same ratio as the angles themselves, 

 so that we can say ACB : ADB : : AD : AC. 



