Complex sentence: The diameter lens, weighing, contains 760 pieces of highly polished prismatic glass, floating in a 7 cwt bath of mercury, and rotating also during the day to reduce the risk of fire from the sun's rays.
Split into simpler sentences: The diameter lens, weighing, contains 760 pieces of highly polished prismatic glass, floating in a 7 cwt bath of mercury. The mechanism is rotating also during the day to reduce the risk of fire from the sun's rays.