practical optician was only less remarkable than his genius as a mathematician. Herschel practiced music as a profession, while giving all his spare time to the grinding of telescope mirrors and to observational astronomy. Ruhmkorff wandered to Paris as a boy of sixteen, and became a porter in the laboratory of a French physicist. In time his name became known wherever the induction coil is used, whether in the investigations of the physicist or in the operations of commercial electricity. Wheatstone adopted the vocation of a maker of musical instruments in preference to grinding Greek and Latin verses at school. This work he continued for many years, achieving world-wide distinction as an original investigator in acoustics, and afterward in optics and electricity.
Younger than Ruhmkorff and Wheatstone, but amply worthy of being classed with them, is Rudolph Koenig, the most distinguished living inventor and mechanician in the domain of acoustics. He was born on the 26th of November, 1832, in Koenigsberg, Prussia. His father was teacher of mathematics and physics in the city gymnasium, where the son as pupil received the usual high-school training, corresponding in some particulars to the academic work in most American colleges. He exhibited much aptitude in physics as well as music; but, being compelled to depend upon his own resources, he went to Paris at the age of nineteen years, to devote himself to the construction of stringed instruments. Here he worked for several years under the direction of the celebrated violin-maker Vuillaume, but at the same time devoted such leisure as he could command to the study of mechanics and physics.
Quite naturally acoustics was the branch of physics which presented most attraction to the young mechanician, and in time it claimed his almost undivided allegiance. Meanwhile his success was such as to warrant him in undertaking business on his own account, so that in 1858 he fitted up a working place for the construction of acoustic apparatus, and in 1859 he issued his first catalogue, containing descriptions and illustrations of the various instruments made by him. Some of these were improvements upon instruments already in use, but many were new, the outcome of Koenig's own ingenuity. This catalogue formed the basis of the subsequent expansions which appeared in 1865, 1873, 1882, and 1889. The last is a volume of one hundred pages, with descriptions of two hundred and seventy-two instruments, in French, English/and German, and including probably everything that is employed in modern acoustic investigation.
It was in 1862 that Koenig began to be known to the scientific world as an investigator. An International Exhibition was held during that year in London, and the indefatigable instrumentmaker was present, not merely for the purpose of displaying the