REPORT ON A LEVISL LINE. 3 



to Portishead, (a distance of eleven miles) and back to Bristol, 

 in order to ascertain the degree of accuracy which could be at- 

 tained in this operation. The total amount of error resulting 

 from this operation was 1*07 inches ; but there appeared grounds 

 for believing that the uncertainty of the result was very much 

 smaller than this quantity ; and this belief has been confirmed 

 by the general course of the subsequent operations. 



3. An excellent telescope level was constructed by Mr. Simms 

 for the Association, to be used on this service, and also a level- 

 ing staff, for which however Mr. Bunt afterwards found it con- 

 venient to substitute one of his own construction. This is de- 

 scribed in the Appendix to this account. 



4. The extremities of the line selected were on the north coast 

 of Somerset and the south coast of Devon, as affording the case 

 where coasts belonging to separate seas could most easily be 

 brought into connexion. A north and south line being thu3 

 obtained, it was proposed to extend the operation to the east- 

 ward, so as to obtain a third point under suitable conditions. 



The first line selected for leveling*, on a careful inspection of 

 the country, was one proceeding from Bridgewater up the river 

 Parret byLangport to Ilminster, Chard, Axminster, and thence 

 to the mouth of the river Axe, which was fixed upon as one of the 

 terminal points where tide observations were to be made. Bridge- 

 water was connected with the sea at the other extremity by a 

 line, which, skirting the Quantocks, reached the shore in the 

 first instance at Stolford opposite the Wick rocks ; but was after- 

 wards carried further to the west in order to reach a more solid 

 rock, and terminated at East Quantocks head near Watchett. 



5. The leveling from Bridgewater to Axmouth was begun 

 May 16, and ended July 8, 1S37. From Bridgewater to Wick 

 rocks the operations of leveling and preparing for tide observa- 

 tions were carried on in October 1837- Tide observations were 

 made at Axmouth from January 4, to February 2, 1838, and at 

 Wick rocks from November 9, to December 9, 1837 j and again 

 at Axmouth, simultaneously with Portishead, July 14 to 21, 

 1838. 



The line thus leveled crossed no very great elevations, and 

 was for the most part very conveniently even. The highest 

 point was at Whites House near Chard, where it attained a 

 height of 280 feet. 



6. The extension of the leveling process to any considerable 

 distance east or west of this line was a matter of difficulty ; the 

 ground in both directions consisting of a series of hills and val- 



• See Plate I., (the map). 

 B 2 



