I attended O Pratts lecture upon Philosiphy at the Tabernacle. It was a dark rainy night. There was quite a Congregation. He treated upon light the two theories by which it is conveyed also its velosity, also vibration Music, sound, its velosoty in air & water and showed how the velosity of light was discovered by a stars Asstronomer while taking an observation of the four Moons of Jupiter for one year he found a variation in the time of the eclipsis of Jupeters Moons according to the distance he was from Jupeter while standing upon the Earth in its different positions + in its ordit in its revolutions around the sun. His lecture * was vary interesting.
He was followed by John Taylor Concerning what the Lord says about his being the light of the Sun and of all worlds & the power by which all things were formed.
[Wilford Woodruff's Journal: 1833-1898 Typescript, Volumes 1-9, Edited by Scott G. Kenney, Signature Books 1993, http://amzn.to/newmormonstudies]