Professor Hall's Lecture.

The subject of Professor Hall's lecture in the Jefferson Physical Laboratory last evening was "The History and Theory of the Steam Engine." The lecture was illustrated by stereopticon views and drawings. The history of the steam engine was traced from the early age down to its present state of perfection. Two hundred years before Christ, a primitive steam engine was used by priests to perform miracles. It took eighteen hundred years to make any advance from this apparatus.

About 1700 a machine was invented to make use of the repellent force of steam. Later a high pressure engine was contrived by Leupold. Single acting atmospheric engines came into use in 1775. These were used entirely for pumping water, as rotary motion had not yet been discovered. In 1800 James Watt, whose memory will ever be held in high esteem both by scientific students and the world at large, invented the double-acting engine, operated by a sliding apparatus, which let the steam into opposite ends of the cylinder. Watt introduced what is termed the expansive work of steam. He contrived to get more out of the steam than heretofore by cutting off the stroke. The mechanism and working of the steam indicator, the planimeter and the sliding and rocking valves were all illustrated by charts and drawings. The lecture closed with a description of the different kinds of modern steam engines.