1871.] Molecules, Ultimates, Atoms, and Waves. 357 



geometrical progression. Thus estimated in hundredths of 

 the millionths of an inch, the shortest aclinic wave would be 

 about 71, and the shortest wave capable of exciting fluores- 

 cence about 23*4 — almost exactly 128 times, or 7 octaves 

 shorter than the length of the wave A.* 



If this be the correct length of the extreme aluminium 

 waves, it will show that the fluorescence which it produces 

 is analogous to a resonance in the case of sound, where a 

 vibrating musical string establishes sympathetic vibrations 

 in another string 7 octaves below it in the musical scale. 

 The very short wave in the ether produced by the aluminium 

 electrodes is not itself visible, but by acting on the molecules 

 of the uranium salt, or on the chemical ultimates composing 

 those molecules, or, perhaps, on the atoms constituting the 

 ultimate of the metal uranium, they establish in them vibra- 

 tions synchronous with themselves. These very rapid vibra- 

 tions give rise by sympathy to others of a lower rate, an 

 octave or more below their own — passing, perhaps, through 

 several successive octaves until there become established 

 in the fluorescent substance vibrations which are syn- 

 chronous with some of those in the ethereal waves of the 

 visible spectrum. There are thus produced in the ether 

 return waves, which are of a length sufficient to affect the 

 optic nerve. 



On the supposition that the extreme aluminium wave 

 is exactly 128 times shorter than the wave A, the proportion 

 which the length of the wave bears to the departure from 

 their points of rest of the individual particles involved 

 in it will be 128 times greater than it is in the case of the 

 A wave. This would make the proportion nearly 43 billions 

 to 1, while the probable number of ethereal particles 

 included in the length of this wave would be about 488 

 millions. 



To convey a more precise idea, let us again apply a 

 magnifying power of a million of billion times. The 

 length of the shortest wave would then be about 3,702,300 

 miles, while the departure of each particle from its point of 

 rest would be only 0^0547 decimal parts of an inch. 



We are now in a position to form a pretty accurate 



* Might not these invisible ultra-violet waves be turned to some useful pur- 

 pose ? Might not the aluminium waves be used for secret telegraphy by night, 

 these invisible rays alone being sent forth in parallel lines by means of a parabolic 

 reflector, while at the receiving station they might be concentrated by another 

 parabolic reflector into a focus on a highly fluorescent surface, by which they 

 would be rendered visible ? Might not also the invisible zinc rays be employed 

 to photograph an object secretly in the dark, by directing them on the object, 

 and receiving them into the camera through a quartz lens ? 



