790 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



the most eligible method of carrying on the survey would be, that of working 

 between any two determined parallels of latitude, till the space between them was 

 completed. Yet this mode would manifestly be subject to some slight innovations, 

 from the necessity of measuring bases in certain stages of the work ; it would be 

 right however to adopt the principle for general practice. Under this idea, it 

 would have been proper to have commenced the operations of this year in Somer- 

 setshire, and to have carried on the triangles from the neighbourhood of the new 

 base there, into the north of Devon. It is mentioned in one of the former 

 accounts, that a zenith sector was formerly bespoken of Mr. Ramsden, by his 

 Grace the Duke of Richmond, for the purpose of aiding the design of measuring 

 the length of a degree of latitude in this country. The pressure of other busi- 

 ness caused Mr. Ramsden to lay aside this instrument, after he had considerably 

 advanced in its construction. The real necessity however for being supplied with 

 an instrument of this description being made known to him, he resolved to take 

 it in hand again, and complete it. Relying on the strength of his assurances to 

 this effect, Col. Mudge determined to relinquish the intention of proceeding to 

 the westward ; and resolved to commence this year's operations, with running up 

 a series of triangles along the meridian of Blenheim. But as the Master-General 

 issued directions, at this time, to survey Essex, and parts of the adjoining coun- 

 ties, in the same manner, and for the same purpose, as Kent had been, Col. M. 

 was obliged to suspend, for a short time, the intention of proceeding with the 

 measurement of a meridional degree, and to devise the best means for carrying 

 his lordship's instructions into execution. 



For this purpose therefore, before any stations were chosen in Essex, the county 

 was very minutely examined ; when it appeared that insuperable difficulties would 

 occur, if the survey were prosecuted with the large theodolite only. The range 

 commencing at Havering Bower, and running to Gallywide Common, cuts off a 

 regular communication between the stations subsequently chosen in the southern 

 and northern parts of Essex. The difficulty resulting from this circumstance was 

 made still greater from the want of success in the endeavours to find one spot on 

 this range, pfoper for a station. The eastern part was, in some degree, found 

 more favourable ; but it was discovered that, even here, the small instrument must 

 frequently be used as a substitute for the large one. Under these disadvantages, 

 the survey commenced in March ; the large theodolite being taken to a station on 

 Hampstead Heath. From Hampstead, the instrument and portable scaffold were 

 carried to Langdon Hill, and thence to Triptree Heath, near Maiden ; whence 

 the party repaired to Highbeech, leaving the remainder of the county to be sur- 

 veyed with the small circular instrument ; which seems to have been done with 

 considerable accuracy. After the necessary observations were made at Highbeech 

 Col. M. proceeded to Shotover Hill, in Oxfordshire ; and before May elapsed had 

 reconnoitred the country. As the distance between Inkpin Hill and Highclere, 

 appeared to be shorter than was necessary for a base on which the northern 



