228 ADDKES3 DELIVERED AT 



school, a sound knowledge of elementary geometry and 

 trigonometry. Belying on this to carry me through, I 

 volunteered to make the required observations. After 

 some hesitation, and a little chaff, a theodolite was con- 

 fided to me. 



The instrument, you know, embraces an accurately- 

 graduated horizontal circle for the measurement of 

 horizontal angles, and a similarly graduated vertical 

 circle for the taking of vertical angles. It is moreover 

 furnished with a formidable array of clamp-screws, 

 tangent-screws and verniers, sufficient to tax a novice 

 to unravel them. My first care before applying the 

 instrument was to understand its construction. This 

 accomplished, I took the field with two assistants, 

 who had to measure uphill and downhill along the 

 sides of large triangles into which the whole country 

 had been previously divided. At the same time 

 angles of elevation had to be taken uphill and angles 

 of depression downhill, and from these the true hori- 

 zontal distance had to be calculated. The heights 

 above the sea-level of the corners of the large triangles 

 had been previously fixed with the utmost accuracy by 

 a very powerful theodolite, and the measurements with 

 my smaller instrument had to come pretty close to the 

 accurate determination to save my work from rejection. 

 Happily I succeeded, though there had been bets against 

 me. The pay upon the Ordnance Survey was very 

 small, but having ulterior objects in view, I considered 

 the instruction received as some set-off to the smallness 

 of the pay. It may prevent some of you young Birk- 

 beckians from considering your fate specially hard, or 

 from being daunted because from a very low level you 

 have to climb a very steep hill, when I tell you that 

 on quitting the Ordnance Survey in 1843, my salary 

 was a little under twenty shillings a week. I have 



