96 PHILOSOPHICAL TRANSACTIONS. [aNNO 1750, 



lo luhich Rockets may be made to ascend, and to what Distance their Light 



may he seen. By Mr. John Ellicott, F.R.S. N° 496, p. 578. 



Soon after the exhibition of the fire-works in the Green Park, on occasion of 

 the late peace, Mr. Robins communicated to the Society an account of the height 

 to which several of the rockets there fired were observed to rise. In this account, 

 after having given a short description of the instrument with which the heights 

 were measured, he observes, that the customary height to which the single or 

 honorary rockets, as they are styled, ascended, was about 465 yards : that 3 

 of them rose to about 550 yards ; and the greatest height of any of those fired in 

 the grand girandole was about 60O yards. He further observed, that supposing 

 rockets are made to ascend 600 yards, or more than a third of a mile, it follows, 

 that if their light be sufficiently strong, and the air not hazy, they may be seen 

 in a level country at above 50 miles distance ; and that, from the nature of the 

 composition, and the usual imperfect manner of forming them, he was of opi- 

 nion that rockets were capable of being greatly improved, and made to reach 

 much greater distances. 



Mr. Robins not having been able to obtain any certain account to what dis- 

 tance any of these rockets were actually seen, and considering the great use that 

 might be made of rockets in determining the position of distant places, and in 

 giving signals for naval and military purposes, he resolved to order some rockets 

 to be fired at an appointed time, and to desire some of his friends to look out for 

 them at several very distant places. The places fixed on for this purpose, were, 

 Godmarsham in Kent, about 50 miles distant from London ; Beacon-hill on 

 Tiptery-heath in Essex, at about 40 miles ; and Barkway, on the borders of Hert- 

 fordshire, about 3S miles from London. 



Mr. Robins accordingly ordered some rockets to be made by a person many years 

 employed in the royal Laboratory at Woolwich ; to which some gentlemen, who 

 had been informed of Mr. Robins's intentions, added some others of their own 

 making. The 27th of September, 17^9, at 8 in the evening, was the time ap- 

 pointed for the firing of them ; but, through the negligence of the engineer, 

 they were not let off till above half an hour after the time agreed on. There 

 were in all a dozen rockets fired from London-field at Hackney ; and the heights 

 were measured by Mr. Canton, Mr. Robins being present, at the distance of 

 about 1200 yards from the post from whence the rockets were fired. The great- 

 est part of them did not rise to above 400 yards ; one to about 500, and one to 

 600 yards nearly. 



A letter received the next day from the Rev. Dr. Mason, of Trinity college, 

 Cambridge, who had undertaken to look out for them from Barkway on the 

 borders of Hertfordshire, informed, that he plainly saw 4 rise, turn, and spread; 



