Complex sentence: A major cause of error in balance wheel timepieces, caused by changes in elasticity of the balance spring from temperature changes, was solved by the bimetallic temperature compensated balance wheel invented in 1765 by Pierre Le Roy and improved by Thomas Earnshaw.
Split into simpler sentences: A major cause of error in balance wheel timepieces was due to the alteration of elasticity of the balance spring from the corresponding temperature changes. This was solved by the bimetallic temperature compensated balance wheel invented in 1765 by Pierre Le Roy and improved by Thomas Earnshaw.