THE SURVEYOR'S LEVEL YESTERDAY AND TO-DAY

Abstract

The last twenty-five years have been remarkable for the progress made in the application of science to instrument design and manufacture. Certain instruments such as the Surveyor's Level appeared twenty-five years ago to have almost reached finality of design; but during the intervening period the improvements made have been of so radical a nature that the progress made has been greater than during any corresponding period. In short, the modern level is a more efficient instrument than its prototype and in spite of reductions in size and weight is, capable of yielding more accurate results with a less expenditure of time and energy. In order to appreciate fully how radical these changes have been, a direct comparison may be made between a first-class level as made twenty-five years ago and a similar instrument as made to-day. Twenty-five years ago it was not possible to obtain a level that could be relied upon to remain in adjustment; one that could be quickly checked and easily corrected offered distinct advantages. The Reversible Level was designed with this end in view; and it is proposed to select such an instrument having an objective aperture of 1·65 inches and to compare it with a modern instrument of the same aperture. The focal length of the telescope of the Reversible Level was 16 inches, and the weight of the instrument with its box was 21½ lbs. (Plate VIII, fig. 1). Many surveyors with long experience of this type still speak highly of its reliability and accuracy; it certainly compared very favourably with other instruments of its period.