[Illustration: FIG. 19.—Webb and Thompson Train-staff Machine.] “When a train is ready to move from _A_ to _X_ the operator at _A_ presses down the lever which is seen at the bottom of the right-hand dial, sounding one bell at _X_, which is for the purpose of calling the attention of the operator at _X_ to the fact that _A_ desires to send a train forward. The operator at _X_ acknowledges the call by pressing the lever on his instrument, sounding a bell in the tower at _A_. The operator at _A_ then asks permission from _X_ to withdraw staff by pressing down the lever before mentioned three times, giving three rings on the bell at _X_, and immediately turns his right-hand pointer to the left, leaving it in the horizontal position pointing to the words ‘For staff,’ indicating that he desires operator at _X_ to release his instrument so that he can take a staff or train order from it. If there is no train or any portion of a train between _A_ and _X_, the holding down of the lever at _X_ closes the circuit in the lock magnets at _A_, which enables the operator at _A_ to withdraw a staff. As soon as this staff is removed from _A_, _A_ turns the left-hand pointer to the words ‘Staff out,’ and in removing this staff from the instrument _A_ the galvanometer needle which is seen in the centre of the instrument between the two dials vibrates, indicating to the operator at _X_ that _A_ has withdrawn his staff. _X_ then releases the lever which he has held down in order that _A_ might withdraw a staff and turns his left-hand indicator to ‘Staff out,’ and with this position of the instrument a staff cannot be withdrawn from either one. “The first method of delivering this staff to the engineer as a train order was to place it in a staff-crane, which crane was located on the platform outside of the block station. With the staff in this position it has been found in actual practice that the engineman can pick it up while his train is running at a speed of 30 miles per hour. A second staff cannot be removed from _A_ nor a staff removed from _X_ until this staff which was taken by the engineman in going from _A_ to _X_ is placed in the staff instrument at _X_; consequently the delivering of a staff from _A_ to the engineman gives him absolute control of the section between _A_ and _X_.