ELECTRIC AND HEAT WAVES NICHOLS AND TEAR 185 



reaches out to the longer electric waves which extend to long radio 

 waves which lie at a distance on our scale of a 100,000 miles to the 

 right — surely an unwieldly chart ! 



A more convenient and adequate method of charting the whole 

 sweep of this comprehensive spectrum is by using geometric inter- 

 vals such as the ascending powers of 2 used in laying off a piano 

 keyboard, on which the wave length of two notes an octave apart are 

 to each other as 2 to 1. Such a spectrum chart is shown in Figure 

 5. On the left are the usual names given to the division of the 

 spectrum. These names are historical in character and belong to 

 the time when the identity of the spectrum as a whole was not 

 realized. To these historic divisions, braces are attached to show 

 approximately their extent on the black strip representing the 

 spectrum. Beyond is shown the number of octaves embraced in 

 each division, and farthest to the right the wave lengths roughly 

 corresponding to these regional boundaries. Of the 53 octaves of 

 the spectrum shown in Figure 8, only 1 octave contains wave lengths 

 visible to the eye, and there is but one remaining region of 3.3 

 octaves between the ultra-violet and X ray spectra in which actual 

 wave-length measurements have not been made. Waves lying in this 

 interval and also radiations beyond the shortest measured X rays and 

 gamma rays indicated have been observed, and the recently dis- 

 covered " quantum " relationships give a sound theoretical basis for 

 calculating these wave lengths, but no interference or diffraction 

 measurements have thus far been carried out in these limited regions. 



Matter under the action of heat is capable of giving off radiations 

 in the so-called infra-red, visible, and ultra-violet spectra; gamma 

 rays are the natural accompaniment of radioactive transformations, 

 and there are various static electric phenomena in the atmosphere 

 which give rise to disturbances resembling fragments of very long 

 electric waves, but X rays and the old and new short electric waves 

 we may still regard as artificial or purely products of laboratory 

 manufacture. 



