A Treatise on Mine-surveying

accuracy accurate alidade axis base-line bearing bore-hole brass calculated centre chain circle City Guilds clamped clinometer coal colliery colour compass construction contour lines cosec cotan cross-wires curve deposit determined direction distance employed engineer equal error EXETER STREET fathoms feet fixed glass graduated ground height hole horizontal Hydraulic inclination instrument iron isogonic lines latitude length line of intersection lode London magnetic bearing magnetic meridian magnetic-needle marked means measured method mine-surveying miner's dial mineral mines needle observations obtained offset Ordnance Survey parallel parallel ruler perpendicular placed plane plate plotting plumb-bob plumb-line plummet pole position protractor representing right angles safety-lamp scale seam shaft side sight spirit-level square staff station station-line strike and dip surface surface-surveys survey tacheometer tacheometry telescope theodolite transit-theodolite traverse triangle tripod tube tunnel underground vernier vernier-plate vertical angles wire yards