The Birmingham age-herald., 1915-04-04
H ROFESSOR A A. MICHELSON, of
 the University of Chicago, has ruled 100000 perfectly straight

the University of Chicago, has ruled 100000 perfectly straight and parallel lines on a piece of metal inches by inches in area.
 This piece of metal is called diff fraction grating, and it's purpose is to split ray of sunlight into the greatest number of shades of color ever seen. It is the basic part of the largest and rnaet perfect spectroscope ever constru
 The spectroscope. as most of
 is an instrument that enables on.
 the different colors of which a r4y at sunlight is composed. In the simplest form of spectroscope the ray is split up by passing through a glass prism. In Professor Michelson's instrument it is split up bv the lines on the diffraction grating.
 The colors composing ray of white sunlight are commonly stated to range from red at one end through orange, yellow, green, blue and indigo to violet at the otheT end. Before the red end of the spectral are the invisible infrared rays, and beyond the violet end are the invisible ultraviolet rays. The visible spectrum is divided into an infinite num- Der of shades of color, and the value Of Professor Michelson's instrument is tlaa 1t measures the largest number of these shades SO far observed The colors in- dicate the nature and proportions of the metals and incandescent materials of which the sun is composed, and reveal other facts about the condition of the luminary., The spectroscope is our prin- cipal means of studying the nature and composition Of the sun, the source of all life and light. The now observations which Professor Nicholson makes with his spectroscopc are therefore, in the truest sense, messages from the sun
 The work of ruling 120, GOO lines on e plate 6 inches by inches is probably the most laborious and delicate task ever carried out. These lines are exactly one eleventhousandth eQuidistant from one another and they are perfectly par allel. So accurate is the paralleling of these lines that if any two of them were extended for a mile there would, not be milliontn part of an inch variation from the parallel
 One of the remarkable uses of this spectroscope is that it will measure the difference between the wave lengths of various colored rays down to millionth part of a centimetre, or one three mil lionth of an inch, recording colors that no human eye ever saw. By means of pho tographic plates many facts will be iearHeu rom tne SpectfOScOp6 that the eye cannot detect.
 The old original prismatic spectro- scope separated a ray of light crudely into seven so-called primary colors-red, orange, yellow, green, indigo blue and violet. The diffraction grating will split the ray into 100000 different shades of color.
 How to draw the lines on the grating was great problem, apart from the tre- mendous labor involved. Several failures were made before satisfactory method of doing the work was reached. The lines are drawn by diamond point. and it had to be done so delicately that there was not the deviation of the breadth of diamond point between any two of the 120,000 lines.
 How to space them accurately was one of the greatest difficulties to be over. come Professor Nicholson tried to do this at first by placing his grating in a mercury bath. He would draw one line and then place the grating edgewise in the mercury bath. Then a measured