upon one's speed

Prepositional phrase

 * 1)  At speed; moving rapidly.
 * 2) * 1662, Thomas Salusbury, Galileo's dialogue Concerning the Two Chief World Systems (Dialogue Two)
 * In case any one, riding a horse that was upon his speed, should let a bowl drop out of his hand, that bowl being fallen to the ground would continue its motion and follow the horses steps, without tarrying behind him.