In prosecuting the work, it was also evident, that the most northerly stars furnished the greatest, and the most southerly the least resulting latitudes. To arrive at the cause of this anomaly, sergeant Steel devoted much of his time to careful investigation, and his efforts and experiments were both ingenious and interesting. These embraced comparisons of the arc with Simms’ dividing engine, by which the non-existence of any sensible error in the divisions of the limb that would account for the observed errors was proved; but it was at the same time clearly ascertained, after a patient examination of the micrometer screws, the levels, the lenses, and the fullest consideration of the law of expansion by heat or contraction either by cold or pressure, that the immediate cause of the disparity arose from the compression of the divided limb by the downward pressure of the upper screw pivot, which, at each station, varied in proportion to the degree of pressure supplied. This was, ever after, a special point of attention with the sergeant, and as, from the construction of the instrument, no absolutely permanent and uniform pressure could be insured at all times, he regulated its extent as well by his judgment as his recollection. It was a rule with him, notwithstanding the apparent errors that might be the result, to register his observations with the strictest exactness. Experience had taught him to expect them as well from local as from indefinable causes. He considered, moreover, that the more perfectly an instrument was constructed, the more honestly would it report the discrepancies of both maker and observer, and that although the conclusions would seem to be a volume of errors, more credit and merit were due to the observer for ascertaining, instead of concealing or covering his errors. Influenced by this novel consideration, he threw an amount of earnestness, care, and faithfulness into his work, that rendered his observations of the highest class for accuracy, and deserving of the fullest confidence. At Southampton he was assisted in the sector service for nearly twelve months by corporal William Jenkins: the one observed from sunset till midnight, and the other from midnight till sunrise. His final observations were at St. Agnes in Scilly, Goonhilly Down near the Lizard Point, North Rona, and Great Stirling—the north-east peak of Scotland. By this series of observations, the arc of meridian, which before terminated at Forth Mountain in the county of Wexford, and Monach in Lewis, was extended to St. Agnes in the south, and to Rona in the north, a small, unknown, and stormy island, about 100 miles west of Orkney.