A fundamental change in working principles was brought about by James Watt. With the close collaboration of Matthew Boulton, he had succeeded by 1778 in perfecting his steam engine which incorporated a series of radical improvements, notably, the use of a steam jacket around the cylinder to keep it at the temperature of the steam and, most importantly, a steam condenser chamber separate from the piston chamber. These improvements increased engine efficiency by a factor of about five, saving 75% on coal costs.