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SPECK, VON STEBNBURG 14 SPECTRUM SPECK VON STERNBURG, HER- MANN, BARON, a German diplomat, born at Leeds, England, in 1852. He studied military and naval science and international law, and served in the Ger- man army in the Franco-Prussian War. He was from 1885 to 1890 military at- tache at Washington. In 1891 he be- came Secretary to the Legation in China. In the year following he served at Buenos Aires and at Belgrade, Serbia. He was appointed First Secretary to the German Embassy at Washington in 1898, and this was followed in 1900 by his ap- pointment as Consul General for British India and Ceylon. He became German Ambassador to the United States in 1903. Largely through his efforts tariff arrangements were perfected between Germany and the United States, in 1906-7. He died in 1908. SPECTROSCOPE, an instrument for observing spectra, or for spectrum analysis. With a single glass prism, the few most prominent lines in a solar spectrum may be seen by using a narrow slit to admit the light, which was the first great improvement made upon Newton's experiment, since a hole or wide slit gives confusion of effect. The second great improvement was to place a collimating lens behind the slit at its focal distance, whereby all the rays from the slit became a parallel bundle before passing through the prism. Finally a small telescope was mounted behind the prism to magnify and define the image thus obtained. The whole arranged on a table, with means of adjusting the col- limating and eye tubes at the proper angles with the prism, forms the ordi- nary single-prism spectroscope. Further prisms may be added to increase the dis- persion. Arrangements are often added for throwing the image of a micrometer scale upon the spectrum, or a reflecting prism may be placed over half of the slit to reflect the solar spectrum into the instrument for comparison with the one under observation. It is in this way that spectra are compared with the solar lines, which are carefully mapped and form the standard of reference. By com- bining prisms of the different refractive and dispersive powers, a strong spectrum may be obtained without deflection. Such prisms may be contained in quite a small tube with slit and lens, and are called direct-vision spectroscopes, which are much used for microscopic observation. Instruments specially fitted for the pur- pose are called star spectroscopes, and there are also special sun spectroscopes, such being necessarily different in prac- tical details from ordinary or chemical spectroscopes. It has become very usual to employ the spectra from diffraction gratings instead of prisms. The higher order spectra thus produced are very pure, and have the advantage of giving the lines in the true position due to their relative wave lengths alone, while prisms compress some groups of lines and ex- tend others, according to the peculiar dispersion of the glass. Spectroscopes thus constructed are called grating spec- troscopes. One of the largest spectroscopes in the world was completed in 1899 by Prof. John A. Brashear, an astronomer of Al- legheny, Pa., for Dr. Hans Hauswaldt, a scientist of Magdeburg, Germany. This powerful concave grating instru- ment is 21 feet long and requires a room about 25 feet square in which to operate it. The grating used on the spectroscope has a six-inch aperture and is ruled with 110,000 lines. So accurately are these lines ruled that none of them varies more than j poo ooo of an inch from the correct position; and so powerful is the instrument that whereas an ordinary spectroscope would show from 100 to 200 lines belonging to the spectrum of iron, this apparatus will reveal more than 2,000. SPECTRUM, in optics, the colored image or images produced when the rays from any source of light are decom- posed or dispersed by refraction through a prism. It has been proved that white- ness is simply a totality of effect pro- duced by the simultaneous effects of many colors falling at once upon the retina. It has been shown (see Re- fraction) how a beam of light is de- flected on meeting at any inclination the surface of a denser medium, and it is obvious that by using a prism with two inclined surfaces, the beam may be per- manently deflected. It is found that each different color, representing a dif- ferent length of wave, is differently re- fracted by the prism, or has its own special index of refraction; hence the prism separates or spreads out, in order, according to their refrangibility, all the different colors of which the beam is composed. This appearance is the spectrum of that particular light. Solids or liquids heated to incandescence — as the particles of soot in a candle flame — always yield an unbroken band of colors shading into one another; this is called a continuance spectrum. Incandescent gases generally yield lines or bands only, and this is a line or banded spectrum. When portions of what would have been a continuous spectrum are intercepted or cut out by an intervening medium this is called an absorption spectrum. Besides the waves of such a length as cause vis-