PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 509 



Although the different rays of the spectrum, according to their posi- 

 tion in the latter, produce predominantly thermal, optical, or chemical 

 effects, it can be shown that the difference in the effects is not caused 

 by an essential difference of the rays, but rather by the different mate- 

 rial condition of the bodies on which the rays act. There is only one 

 kind of radiation, which however according to the number of oscilla- 

 tions of the SBther-atoms and the difference of the irradiated matter, 

 manifests itself in various ways in the effect. Heat, light, and chem- 

 ically acting rays are in essence identical, and they become only distin- 

 guishable when the kinetic energy of their aether oscillatious is transmit- 

 ted to the material particles of a suitably disposed body. For instance, 

 every ray of light is also a ray of heat ; but the so-called obscure rays 

 of heat and rays of light differ only in the number of their oscillations ; 

 otherwise they are quite the same. The rays of light alone are able to 

 excite the ends of the optical nerves to optical action, while the visible 

 as well as the invisible (so-called obscure) heat rays cause an increase 

 of temperature in those substances by which they are absorbed. 



In order that rays may act upon a body which they strike, it is indis- 

 pensable that they should be absorbed, The absorption of heat, light, 

 or chemical rays is a transmission of kinetic energy from the oscillating 

 rether atoms to the molecules, and, in chemical effects, to the atoms of 

 master. Although the equivalent of a given quantity of light has not 

 yet been determined, it is certain that through the absorption of light 

 rays, substances become heated, and the chemical action of the light 

 rays augments precisely as the absorption of the latter ; the law of the 

 conservation of energy finds its application in this, though the quanti- 

 tive proof is wanting as yet. 



The wave, or undulatory theory of light, explains the phenomena in 

 a very simple manuer, as we demonstrated in the example of the spec- 

 trum ; it reduces the radiation of light and heat to a common principle. 

 The theory of the emission of luminous matter had to assume as many 

 variously colored luminous atoms as the innumerable colored rays in 



This eminent physicist has certainly proved that the accepted generalization is at 

 least fallacious, and hased on insufficient data. From the enormous distortion 

 necessarily incident to every refraction spectrum, (as shown by reference to an 

 arithmetical scale of wave-lengths, or by the simpler expedient of comparison with 

 a diffraction spectrum,) Dr. Draper has pointed out that computing from the arith- 

 metical center of the spectrum, — the point of maximum illumination in the yellow 

 band — (near the sodium line I)), the lower side of the scale is compressed into about 

 half its just extent, while the upper side is expanded to about double its proper range. 

 (Am. Jour. Sci. Sept. 1872, vol. iv, pp. 161-175.) And as this distortion goes on rap- 

 idly increasing from the mean portion, the extra optical rays are many times condensed 

 beyond the red extremity, and many times dilated beyond the violet extremity. Ac- 

 cordingly the ''heat-curve," familiarly exhibited by popular writers and lecturers, is 

 simply an egregious "anamorphosis." Secondly, Dr. Draper has shown that the 

 actinic or chemical euergies of the solar ray are distributed throughout the spectrum 

 (visible and invisible), provided that the observer's attention is not coutincd (as usual) 

 to the decompositions of silver salts. (Am. Jour. £>ci. Jan. and Feb., 1873, vol. v. pp. 

 25-38; and pp. 91-98.)— Ed.] 



