PHILOSOPHICAL TRANSACTIONS. 



241 



VOL. LXXXVII.] 



depressions of the several stations, above and below each other, taken in minutes 

 and seconds ; from which is derived the following table of terrestrial refractions. 



To 

 To" 



1 2 

 1** 





Between ° t f ai»« 



Maker and Kit Hill \ 



Butterton and Kit Hill £ 



Bindown and Lansallos \ 



Nine Barrow Down and Black Down . 



Maker and Lansallos 



Maker and the Bolt Head -fa 



Carraton Hill and Bindown 



Karnbonellis and St Buryan 



Maker and Bindown 



Hensbarrow and the Deadman 



St. Agnes' Beacon and the Deadman y'-j 



St. Agnes' Beacon and Karnminnis -fa 



Dumpdon and Cawsand Beacon t'-j 



Haldon and Cawsand Beacon . . . t ^ 



Kit Hill and Bindown fa 



Carraton Hill and Hensbarrow T ' T 



Lansallos and the Deadman -fa 



Hensbarrow and St. Agnes' Beacon -fa 



Karnbonellis and Karnminnis tV 



Furland and Haldon -fa 



Butterton and Maker -fa 



Butterton and Carraton Hill -fa 



The mean refractions were found by the following rules. 1 . Reduce the eleva- 

 tions, or depressions, to the place of the axis of the telescope at each station, by 

 adding or subtracting, as the case may require, the angle at the place of observation, 

 subtended by the vertical height between the object, whose elevation or depression 

 was observed, and the axis of the telescope when at that station.* 2. Then, if 

 both are depressions, subtract their sum from the contained arc, and half the re- 

 mainder is the mean refraction. 3. If one is a depression and the other an eleva- 

 tion, take their difference. Then, if the depression is greater than the elevation, 

 subtract the difference from the contained arc, and half the remainder is the mean 

 refraction. But if the elevation is greatest, add the difference to the contained arc, 

 and half the sum is the mean refraction. 



Next follows a table containing the heights of the stations, viz. 



Between °1&YZ: 



Maker and Carraton Hill -fa 



Karnbonellis and the Deadman -fa 



Karnbonellis and St. Agnes' Beacon -fa 



Karnminnis and St. Buryan -fa 



Hensbarrow and Bodmin Down T ' 7 



Lansallos and Bodmin -fa 



Butterton and the Bolt Head -fa 



Haldon and Charton Common -fa 



Rippin Tor and Cawsand Beacon -J T 



Black Down and Bull Barrow ^fa 



Black Down and Pilsden Hill T i T 



Black Down and Charton Common -fa 



Lansallos and Hensbarrow -J T 



Rippin Tor and Haldon 



Butterton and Furland 



Butterton and Rippin Tor ^ 



Kit Hill and Carraton -fa 



Pilsden Hill and Charton Common ^ 



Wingreen and Bull Barrow 7 » T 



Lansallos and Carraton Hill J^- 



Haldon and the Horizon of the Sea -fa 



Pilsden Hill and the Horizon of the Sea . . -i. 



Heights 



Stations. Feet. 



Black Down 817 



Charton Common 582 



Little Haldon 818 



Rippin Tor 1549 



Furland 589 



Butterton t 1203 



Maker Heights 402 



Bull Barrow 927 



Mintern Hill 891 



Pilsden Hill 934 



Dumpdon 879 



Cawsand Beacon 1792 



Heights. 



Stations. Feet. 



Bolt Head 430 



Kit Hill 1067 



Bindown 658 



Carraton Hill 1208 



Lansallos 514 



Bodmin Down , 649 



Hensbarrow Beacon 1026 



The Deadman 379 



St. Agnes' Beacon 599 



Karnbonellis 822 



Karnminnis 805 



St. Buryan 415 



* For example. At the station on Hensbarrow., the ground at Bodmin Down was depressed 31' 27" ; 

 the distance of those stations is 47337 feet j and the axis of the telescope was 5 J feet above the ground 

 VOL. XVIII. I 1 



