142 BULLETIN OF THE 



daughter chemistry, as the most subtile and delicate of all her re- 

 agents. From this method of observation we have learned that 

 each of the elements when its molecules are shocked, rings out its 

 own peculiar series of oscillations, as if by specially adjusted tuning- 

 forks, each responsive only to the groupings of its own established 

 periodicities. Newton first taught us that definite refrangibility in 

 the spectrum signifies simply definite periodicity ; and he also com- 

 puted the data which determine the values of these periodicities.* 



The known wave-lengths of different colored light divided by 

 their known velocity of propagation, give us the inconceivable 

 rapidity of from 390 to 750 billions per second,f as the number oi 

 atomic impulses transmitted by the aether and appreciated by the 

 eye. Although this compass is somewhat less than an " octave," 

 the entire range of the visible and invisible spectrum comprises 

 more than three octaves. This extraordinary rate of vibration, no 

 less than its remrakable uniformity, sufficiently establishes the fact 

 that the motions of the molecule ceaselessly varying in velocity, and 

 wholly irregular in length and frequency of excursion, take no part 

 whatever in producing aetherial undulations. It is only to the con- 

 stituent parts or ultimate atoms of the flying molecule that the rhyth- 



* Newton's Optics. 1704 : book n, part i, obs. 6. When shortly after his 

 election to the Royal Society, Newton in a letter to the Secretary — Henry 

 Oldenburg, (dated January 18, 1672,) proposed to offer a communication to 

 that Society respecting his optical analysis, he spoke of it as " being the 

 oddest if not the most considerable detection which hath hitherto been made 

 in the operations of nature." (Birch's History of the Royal Society. 1757: 

 vol. in, p. 5.) Although a century and a quarter elapsed before the spec- 

 tral lines were first detected by W. H. Wollaston, (Phil. Trans. Roy. 

 Soc. June 24, 1802: vol. xcn, p. 365;) Newton was fully aware of the 

 necessity of employing a very small hole or luminous image for obtaining 

 a pure spectrum, and he pointed out that a narrow slit is still better ; " for 

 if this hole be an inch or two long, and but a tenth or a twentieth part of 

 an inch broad, or narrower, the light of the image will be as simple as be- 

 fore, or simpler, and the image will become much broader." (Optics: 

 book I, prop, iv.) For delicate observations Newton appears to have been 

 compelled to rely on the services of an assistant ; and thus he missed the 

 consummation of his "oddest and mo3t considerable detection of nature's 

 operations " — the spectroscope. 



f A billion (as is sufficiently indicated by the term itself) is the " second 

 power of a million ;" not (as is commonly taught in school-book numera- 

 tion) the third power of a thousand, or the second power of an impossible 

 number ; — a surd 



