088 Transactions of the American Institute. 



that a prism of glass would refract and disperse a ray of sunlight, giving 

 rise to an image formed of a series of colors called the spectrum. He 

 discovered that the light of the sun consisted of seven different parts ; 

 but how the prism sepai-ated these he did not explain. There is 

 another way of separating liglit, and that is by Fraunhofer's lines as 

 seen in the spectrum by the aid of a telescope. These lines are so 

 close togther as to make 7,000 to the inch. (The doctor here exhibi- 

 ted Fraunhofer's lines). Where a thermometer is placed in the rays 

 of the spectrum, the j^ellow light shows a slight increase of tempera- 

 ture, and the orange more, and the red the highest heat. In the other 

 rays there is hardly any perceptible heat. Photographers know that 

 the blue and violet have the greatest photographic effect. The great- 

 est strength, photographically, is in the violet ; the greatest heating 

 power is in the red ray. Light is transmitted with enormous velocity. 

 It takes eight minutes for the light of the sun to reach the earth, so 

 the velocity of light from the sun is 200,000 miles in a second. The 

 undulator}'^ theory of light, first proposed by Huyghens, is now uni- 

 versally adopted. Our study of sound has given us a key to the 

 theor}^ of light. 



Light consists of waves, just as sound is transmitted, which moves 

 with a less velocity than light. The length of a wave of light is 

 about an eight hundred-millionth part of a millimetre. AVhen we 

 divide the length of the wave with the light we get the number of 

 waves in a second. Suppose two waves of sound follow each other 

 in one second, we have 750,000,000,000 of vibrations in a single second. 

 The velocity of undulations producing red light is 472,000,000,000 of 

 vibrations in a second. The vibrating medium cannot vibrate at a 

 lower or higher velocity tlian this ; so it always gives this red color. 

 Color is only an impression that is given to us. There are persons 

 who are color blind ; in the same way we have persons who can- 

 not distinguish the vibrations of sound, and know scarcely one 

 sound from another. That M'e see a color is only an objective 

 fact. 



The diagram here shown is the spectroscope line for calcium, which 

 shows that the sun contains calcium. Here again we have the lines 

 for gold, silver, etc., which proves to us that the sun contains these 

 and many other metals. The Geissler tubes have been shown here 

 before. Those tubes exhibited that evening were filled with gasses of 

 different kinds, Avhich give various colors when electricity is passed 

 through them. Hydrogen is very white. The spectrum of oxygen 



