“This occupation led me to inquire into the great trigonometrical survey then carried on by Colonel Mudge, especially that part of it which related to the neighbourhood of Birmingham, my chief object being to ascertain what records would avail for our map, and what further steps it would be needful for me to take to complete the work. With this view I procured his report, and studied it with care, finding it more interesting than any novel. I read with particular interest the part describing the measurement of the great base line on Hounslow Heath by his predecessor, General Roy; and I gathered from it that my own base lines, taken one on our playground and the other on the opposite side of Birmingham, were far too short, the longer extending to only one hundred-and-thirty feet. I therefore resolved to recommence my work, and not only to take a much longer base line, but also to measure it as accurately as I could. I now give a passage taken from my Journal. “‘I accordingly procured some long deal rods and three stools for the purpose of measuring a line with great accuracy. The stools are made to rise and fall, and somewhat resemble music-stools; this construction was necessary, in order to place the rods always upon the same level.[41] “‘I chose Bromsgrove Street as the situation of the base, on account of its remarkable levelness, and the number of objects which are visible from different parts of it. The base extends from the corner of the Bell Inn, on the right-hand side of the Bristol Road, and opposite to the end of Bromsgrove Street, to the wall at the north-eastern end of Smithfield; being nearly half a mile in length, and so admirably situated with respect to the objects, that there is not a single obtuse angle upon it. “‘Besides measuring with the rods, I surveyed the line twice with a land chain, properly adjusted, and after making every allowance for the elongation of the chain during the admeasurement, I found the difference in the total length of the base, which is nearly half a mile, to be only three-quarters of an inch. When the survey is completed, I intend to write an account of it, which will be found among my manuscripts.[42] “‘I have thought of publishing parts of it in some of the magazines, particularly a relation of a new mode of using the theodolite, which I have invented. This mode increases its power exceedingly.’ “In performing this work it was of course necessary to avoid the daily traffic, which would have disturbed our operations; and, as my Journal shows, my class and I, during the three days occupied in the process, viz., May the 25th, 27th, and 30th, rose the first day at three, the second at five minutes before three, and the third at five minutes past two.