I broke a little bit off the colourless end of the Glass Tube and placed it in the focus of the Burning Glass leaving it there several minutes, but no change was produced in its Colour. After examining it I exposed it again to the collected rays of the Sun without observing the least change in its colour, but touching it with the end of a small splinter of Cedar wood the wood took fire and the Glass immediately became a fire red. I am Dear Sir your very humble Servant