Heights of the principal Hills of Dent, tyc. Yorkshire. 197 



when the variable part of the refraction is at its negative maxi- 

 mum*. The refraction between Noughtberry Hill and the 

 much lower hill Pendle, comes out, it is true, very considerable 

 (1-16*5); but as the day on which the observations were made 

 was of extraordinary clearness, which is generally attributed 

 to the rate of decrement of temperature in the atmosphere be- 

 ing much less than wanted, the refraction would in consequence 

 exceed its mean value. 



The register of the observations will require explanation. — 

 The first column gives the time at each observation ; the se- 

 cond, the name of the hill of which the ground at the summit 

 (Pen-y-gent excepted) was observed ; the third, its elevation E 

 or depression D as read off on the left index ; the fourth, the 

 half difference of the corresponding reading by the right in- 

 dex + the constant error of the instrument and the variable 

 one of the levels, forming together what is termed the error 

 of collimation, additive to, or subtractive from the given read- 

 ing according to* its prefixed sign. (Were the graduations 

 perfect and the adjustments of the cross lines and levels un- 

 affected by variation of temperature, the error of collimation 

 should be a constant quantity.) The last column contains the 

 difference of level of the ground at the station (Pen-y-gent 

 excepted) and the summit of the observed hill, the latter being 

 higher or lower than the station according as the difference is 

 marked H or L. 



At Whaw Fell. 



Height of Eye 3-5 feet. 



Feet. 

 372-6H. 

 377-1 

 82-4 

 184-0 

 356-8 



537-9 



388*8 



V513-7 



579-4 

 165-6 

 451-2 



* The mornings were generally slightly frosty. 



Height 



