J . fa * , / R E B , 



n ** , />iv ^^, ^ ^ ^ 



By the last formula the following Table was computed 



TABLE, 



Shewing the distance of the farthest risible point in miles 

 from the top of a given height, taking into account the 

 tion. 



Height in feet. 

 500 



700 

 1COO 

 1500 

 2000 

 2500 

 3000 

 3500 

 4COQ 

 5000 

 6030 

 7000 

 8000 

 9000 

 10000 

 15000 





that can le teen 

 effect of refrac. 



Dist. in miles, 

 , 29.5 

 . S5.0 

 . 41.8 

 ,51 



.79 

 . 83 

 .94 

 , 102 

 . 110 

 . 118 

 . 125 

 . 132 

 . 162 

 , 187 



Ex. 1. The topmast of a ship 50 feet high was just visible to a specta- 

 tor situated 20 feet above the level of the sea ; required the distance of 

 the ship, 



Feet. Miles. 



By table 50 ..., give 9.35 



20 do 5.91 



Required distance 15.26 



Ex. 2. The summit of Mouna Roa (whose height is supposed 15,000 

 feet) was observed at 180 miles distance ; required the height of the ob. 

 server. Miles. 



Observed distance 180 



Distance due to 15000 feet 162 



Difference 13 



which answers to a little lees than 200 feet altitude. 

 241 



