The spectroscope is the improved instrument by which the diffracting prism is best employed in producing the spectrum.  The reader no doubt has seen a spectroscope, and has observed its beautiful work.  In this place we pass, however, from the instrument of production to the spectrum, or analyzed result, as the same is shown on a screen.  There the pencil of white light falling from the sun is spread out in the manner of a fan, presenting on the screen the following arrangement of colors:  red, orange, yellow, green, blue, indigo and violet.

This order of colors, beginning with red, starts from that side of the spectrum which is least bent from the right line in which the white ray was traveling.  The violet rays are most bent.  The red rays are thus said to be at the lower edge of the prism, and the violet rays at the upper edge.  Below the red rays there are now known to be certain invisible rays, as of heat and electricity.  Above the violet rays are other invisible rays, such as the actinic influence.  In fact, the spectrum, beginning invisibly, passes by way of the visible rays to the invisible again.  Nor can any scientist in the world say at the present time how much is really included in the spread-out fan of analyzed sunlight.

Thus much scientists have known for some time.  Certain other facts, however, in connection with the solar spectrum are of greater importance than are its more sensible phenomena.  It was in the year 1802 that the English physicist, William Hyde Wollaston, discovered that the solar spectrum is crossed with a large number of dark lines.  He it was who first mapped these lines and showed their relative position.  He it was also who discovered the existence of invisible rays above the violet.  Twelve years afterward Joseph von Fraunhofer, of Munich, a German optician of remarkable talents, took up the examination of the Wollaston lines, and by his success in the investigation succeeded in attracting the attention of the world.

This second stage in scientific discovery is generally that which receives the plaudits of mankind.  It was so in the case of Fraunhofer.  His name was given to the dark lines in the solar spectrum, and the nomenclature is retained to the present time.  They are called the “Fraunhofer lines.”  It was soon discovered that the lines in question as produced in the spectrum are due to the presence of gases in the producing flame or source of light.  It was also discovered that each substance in, the process of combustion yields its own line or set of lines.  These appear at regular intervals in the spectrum.  When several substances are consumed at the same time; the lines of each appear in the spectrum.  The result is a system of lines, becoming more and more complex as the number of elements in the consuming materials is increased.