Nature . spectroscope ./, slit; t /, scale illumin- flames to be ; /, observinR telesc ated by h ,nnd reflected by the second surface of the prism into green, as the case may be, will go to build up an imageof the slit in the appropriate part of the spectrum, andthat the image thus built up will take the form of a lineor circle, accortling to the slit we use. Many chemical substances, salts or various metals,become luminous by inserting them into llames, as wehave treated tomniDn salt (chloride of sodium). Witheach metal tin- colour imparted to the flame is resulting
Nature . spectroscope ./, slit; t /, scale illumin- flames to be ; /, observinR telesc ated by h ,nnd reflected by the second surface of the prism into green, as the case may be, will go to build up an imageof the slit in the appropriate part of the spectrum, andthat the image thus built up will take the form of a lineor circle, accortling to the slit we use. Many chemical substances, salts or various metals,become luminous by inserting them into llames, as wehave treated tomniDn salt (chloride of sodium). Witheach metal tin- colour imparted to the flame is resulting spectrum is called a discontinuous spectrum,because it is only here and there that images of the slitare produced ; because some coloured rays, and not all,are present. February i6, i NA TURE 573. The usual laboratory arrangement for observing the inch. The unit of wave-length usually employed is thespectra of flames is shown m the woodcuts. | ten-millionth of a millimetre. These wave-lengths get Further, the system of images of the needle (or slit) | shorter as we pass from the red to the violet. So much then in general for the radia-tions given out by light sources, and themanner in which the spectroscope showsthem, and the student records theirpositions. Spectrum analysis was establishedwhen experiment proved that no twosubstances which give a line spectrumgive the same order of lines from oneend of the spectrum to the other; in otherwords, the line spectrum of each chem-ical substance differs from that given byanv other Fig. 4.—The spectrum of .1 complicited light-source .is seen with a circular and a line slit. t_r .1 • r 1 ... Here then is one of the secrets of the new power of investigation of which the varies for each substance, and it is on this ground that spectro
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