The coupling illustrated in the figure was designed by Obach. It dates from 1870 and was probably the first device of this kind ever made. It was an application of the principle of the eccentric, and was exceedingly simple. The rope rested on roller b, and the eccentric a turned until it gripped the rope which travelled in the direction of the arrow (see drawing), and thereby helped to tighten the eccentric against the rope \ but as the grip on the carrier depended solely on the friction between rope and eccentric, it was not very great. The method of coupling or uncoupling was exceedingly simple, being effected by eitherdropping or lifting lever c.