Trengrouse had a small competence, besides his trade, and he devoted every penny that he could spare to experiments, first in the construction of a lifeboat, but without satisfactory results. The King's birthday was celebrated at Helston with fireworks on the green; and as Henry Trengrouse looked up at the streak of fire rushing into the darkness above and scattering a shower of stars, it occurred to him, Why should not a rocket, instead of wasting itself in an exhibition of fireworks, do service and become a means of carrying a rope to a vessel among the breakers? When a communication has been established between the wreck and the shore, above the waves, it may become an aerial passage along which those in distress may pass to safety. Something of the same idea had already occurred to Lieutenant John Bell in 1791, but his proposal was that a shot with a chain attached to it should be discharged from a mortar. Captain George William Manby had his attention drawn to this in February, 1807, and in August of the same year exhibited some experiments with his improved life-preserving mortar to the members of the Suffolk House Humane Society. By the discharge of the mortar a barbed shot was to be flung on to the wreck, with a line attached to the shot. By means of this line a hawser could be drawn from the shore to the ship, and along it would be run a cradle in which the shipwrecked persons could be drawn to land. Manby's mortar was soon abandoned as cumbrous and dangerous; men were killed during tests; notwithstanding which he was awarded, £2000. The great merit of Trengrouse's invention was that the rocket was much lighter than a shot from a mortar, and was, moreover, more portable, and there was a special line manufactured for it that would not kink, nor would it snap, because the velocity of the rocket increased gradually, whereas that from a discharge of a mortar was sudden and so great that the cord was frequently ruptured. The distinctive feature of Trengrouse's apparatus consisted of "a section of a cylinder, which is fitted to the barrel of a musket by a bayonet socket; a rocket with a line attached to its stick is so placed on it that its priming receives fire immediately from the barrel";[9] whereas a metal mortar could not be conveyed to the cliff or shore opposite the scene of disaster without being drawn in a conveyance by horses, and where there was no road with the utmost difficulty dragged over hedges and ploughed fields by men. Not only so, but a shot discharged by Captain Manby's mortar was liable to endanger life. Wrecks generally happened in the dark, and then the shot would not be visible to those on the wreck. But Trengrouse's rocket would indicate its track by the trail of fire by which it was impelled, and could be fired from either the ship or the shore.