The throttle-valve is opened or closed by turning a grooved vertical pulley by means of an endless cord, called the telegraph, passing round another pulley fixed upon the " headache-post," and is thus under the control of the driller working in the derrick.
To telescope the jars for the next blow coming up. A skilful driller never allows his jars to strike on the downstroke, they are only used to jar down when the tools stick on some obstruction in the well before reaching the bottom, and in fishing operations.
While there he published his System der analytischen Geometrie, auf neue Betrachtungsweisen gegrundet, and insbesondere eine ausfuhrliche Theorie der Curven driller Ordnung enthaltend (Berlin, 1835).
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