AMONG the many men of science of German birth who during last century made England their home was Herman Johann Philipp Sprengel, F.R.S., the centenary of whose birth occurs on August 29. Born at Schillerslage near Hanover, he studied physics and chemistry at Gottingen and Heidelberg, taking the degree of Ph.D. in 1858. In January 1859 he came to England and for three years was associated with Brodie at Oxford. He then settled in London and engaged in research work at the Royal College of Chemistry and in the laboratories at Guy's and St. Bartholomew's Hospitals. From 1865 until 1870 he was chemist at Farmer's chemical works in Ken-nington, after which he devoted himself mainly to his own inventions. He was elected F.R.S. in 1878 and in 1903 the title of professor was bestowed upon him by the German Emperor. He died suddenly on January 14, 1906. Sprengel will always be remem bered for his invention in 1865 of the dynamic mercury pump which made possible the evacuation of Swan's and Edison's electric glow lamps, Crookes's radiometer and Rontgen's apparatus, and for his improvements in explosives. In 1871 he took out patents for a class of explosives which were non-explosive during manufacture, storage and transport, but for want of encouragement he allowed the patents to lapse. His explosive ‘rack-a-rock’ was used in 1885 for removing the Flood Rock Reef which obstructed the entrance to New York Harbour at Hell Gate, some 300,000 lb. of the explosive being used. He also devised a U-tube for the determination of the density of liquids, introduced the use of a finely divided spray of water in the place of steam in sulphuric acid chambers and was the first to direct attention to the value of picric acid as an explosive.