A party of sixteen non-commissioned officers and men, afterwards increased to nineteen of all ranks, under sergeant James Steel, was detached on the 1st May with sufficient camp-houses, equipage, and stores, to carry out the remeasurement of the base line on Salisbury Plain, by means of the compensation bars invented by General Colby.[45] No man or officer on the survey had ever seen the apparatus in position before; and sergeant Steel, therefore, has the credit of acquiring a full knowledge of the adaptation and uses of the various instruments belonging to the apparatus, unassisted by the teaching of any practician. This he achieved by more than three months’ unwearied study of some manuscript records on the subject, and by closely observing the results of a series of experiments which he conducted. During the first fortnight, the line, six miles and three-quarters in length as the crow flies, was three times measured with the chain, marked off, cleared of wood, furze, and other obstacles, and again roughly surveyed. The little wooden encampment of the detachment was by this time in excellent order; and, after three days’ tedious work in testing the apparatus by comparison with the standard bar, the first compensation bar in the remeasurement was laid at Beacon-hill. Owing to the steepness of the ground, and other causes, progress over the hill was both slow and wearisome; but having once mastered the descent, the operation throughout its length presented less difficulties than were at first encountered. From time to time the sergeant communicated to the ordnance map office at Southampton the obstacles, both physical and instrumental, he met with in his progress, and the contrivances he resorted to, to overcome them. The journal so sent was full of practical instruction, of a kind to be easily acquired on future reference, and was replete with interesting information.