116 Travis. Acad. Sci. of St. Louis. 



day. He stirred up the ethereal ocean by making electrical 

 disturbance between spheres 30 cm. in diameter. The ether 

 waves which he produced were 5.55 meters in length. When 

 the disturbance is produced on smaller spheres, the wave- 

 lengths are found to be shorter. In order to reduce the 

 length of these Hertz waves to the length of light waves, so 

 that they would become luminous, the bodies which are elec- 

 trically disturbed must have dimensions such as Kelvin has 

 computed for the atoms. An electrical disturbance of elec- 

 trically charged atoms therefore involves the setting up of 

 ether waves which affect the eye and which are called light 

 waves. It is evident that in great solar outbursts, ether dis- 

 turbances of large magnitude must be produced in order to 

 account for the distortions of the earth's magnetic field, which 

 are so frequent in the time of solar activity. It is possible 

 that a blast from, a great gun might have an appreciable effect 

 upon a neighboring magnetic needle, of small moment of 

 inertia and in a zero field.* 



Spectrum analysis has been wholly developed during the 

 last century. Fraunhofer discovered the dark lines in the 

 solar spectrum in 1817. It was not until Bunsen and Kir- 

 schoff took up the matter about 1866 that the significance of 

 the dark lines was suspected. Bright line spectra had been 

 observed, and the coincidence of the dark lines of the solar 

 spectrum with the bright lines due to certain metals, was 

 finally found to indicate that the metals whose light was 

 absent in sunlight, were present in the sun. The continuous 

 spectrum is made up of an infinite series of overlapping 

 images of the slit. The dark lines indicate that images are 

 wanting. The particular light which iron vapors yield when 

 heated has been partially quenched by the cool iron vapors 

 lying above the most strongly luminous layers of the sun. 

 These dark lines are displaced in the spectrum if either the 

 radiating substance or the earth is in motion which changes 

 the distance between the eye and the radiant mass. The 

 phenomenon is precisely similar to the one in sound where 



* This experiment yields appreciable effects, but it is so far complicated 

 with the magnetic reaction of the steel barrel of the gun, and possibly with 

 Rowland effects. 



