The lecture discussed the structure of metals, mainly as observed under a microscope. Dr. H. Sorby first applied the microscope to metal study in 1864, but this work was not followed for nearly 25 years. In the last 15 years, it has been pursued with great enthusiasm, especially in Dr. Sorby's hometown. Cambridge contributed significantly, with work by Rosenhain, Humfrey, Neville, and Heycock. The lecture showed microphotographs of polished and etched metal surfaces, revealing the structure of pure or nearly pure metals, composed of irregular grains with polygonal boundaries. Each grain was a true crystal with a regular arrangement of particles. When etched, the facets of these grains were visible, and their brightness varied with the angle of light. Grains grew from nuclei, with boundaries formed by the interaction of grains during growth. In some metals, grains formed during crystallization from the liquid state, while in others, like iron, re-crystallization occurred after solidification, leading to less regular boundaries and more intimate interlocking between grains. The structure could be fine or coarse, with coarse structures in specially pure metals under slow cooling. An example of lead with large grains was shown. The lecture also discussed the effects of stress on metals, showing slip lines in various metals, and how fatigue leads to breakdown in metals. Alloys were discussed, with different ways in which two constituents could combine. Eutectic alloys showed zebra-like markings due to alternating deposition of constituents. The lecture also covered the structural changes in metals at atmospheric temperatures after severe straining, and compared the structure of glacier ice to that of metals, noting that both undergo slow structural changes. The gas supply of the metropolis was also discussed, with a committee examining the statutory requirements for gas purity and illuminating power. The committee found discrepancies in testing methods and recommended that tests be conducted directly from the main gas supply to testing places. The gas companies resisted this, leading to some testing places remaining closed. The committee believed this requirement was reasonable and suggested it be made statutory.The lecture discussed the structure of metals, mainly as observed under a microscope. Dr. H. Sorby first applied the microscope to metal study in 1864, but this work was not followed for nearly 25 years. In the last 15 years, it has been pursued with great enthusiasm, especially in Dr. Sorby's hometown. Cambridge contributed significantly, with work by Rosenhain, Humfrey, Neville, and Heycock. The lecture showed microphotographs of polished and etched metal surfaces, revealing the structure of pure or nearly pure metals, composed of irregular grains with polygonal boundaries. Each grain was a true crystal with a regular arrangement of particles. When etched, the facets of these grains were visible, and their brightness varied with the angle of light. Grains grew from nuclei, with boundaries formed by the interaction of grains during growth. In some metals, grains formed during crystallization from the liquid state, while in others, like iron, re-crystallization occurred after solidification, leading to less regular boundaries and more intimate interlocking between grains. The structure could be fine or coarse, with coarse structures in specially pure metals under slow cooling. An example of lead with large grains was shown. The lecture also discussed the effects of stress on metals, showing slip lines in various metals, and how fatigue leads to breakdown in metals. Alloys were discussed, with different ways in which two constituents could combine. Eutectic alloys showed zebra-like markings due to alternating deposition of constituents. The lecture also covered the structural changes in metals at atmospheric temperatures after severe straining, and compared the structure of glacier ice to that of metals, noting that both undergo slow structural changes. The gas supply of the metropolis was also discussed, with a committee examining the statutory requirements for gas purity and illuminating power. The committee found discrepancies in testing methods and recommended that tests be conducted directly from the main gas supply to testing places. The gas companies resisted this, leading to some testing places remaining closed. The committee believed this requirement was reasonable and suggested it be made statutory.