of a triangular prism of glass which breaks up the white light of the sun into its component colors of red, orange, yellow, green, blue, indigo and violet. The other and better way is by the use of a grating. Such at. instrument is made by ruling on the surface of a plane or concave mirror many thousand tine lines separated by equidistant intervals. The writer had mounted for his use at the eclipse five spectroscopes, two being prisms, the others gratings. By means of these a great variety of problems were attacked, such as the constitution of the atmosphere immediately surrounding the sun and the heights in miles to which the different gases extend above the sun's surface, the nature of the gases that go to make up the beautiful corona, the amount of heat and energy of the corona, etc.
