APP. E.] 



APPENDIX 



521 



E. — To show tliut the Distance of Horizon in EwjUsK Allies 



= »/-]— height ill feet, 



Let r be radius of earth. 



h hf-iglit of observer in feet. 

 d distance of horizon. 



Fig. 121. 



= -^ A very nearly ; 



This is the distance disrecarding refraction, which has the effect of 

 increasing the distance of the visible horizon. If having found d as 



above, we subtract y^ of itself from it, the remainder will be the true 



distance in sea miles very nearly, with the effects of refraction taken 

 into consideration. 1 



