576 BIBLIOGRAPHY OF HERSCHEL's WRITINGS, 



Herschel) W.: Sykopsis of the Wkitixgs of — Continued. 



A. D. Vul. P. 



some of these lieat-makiug rays may not have a power of render- 

 ing objects visible, superadded to their now already established 

 power of heating bodies." 



1800 90 508 " It has been shown that the effect of heat and of illumination may- 

 be represente<l by the two united spectra which we have given." 

 "Now when these are compared it appears that those who would 

 have the rays of heat also to do the office of light must be obliged 

 to maintain the following arbitrary and revolting positions, namely : 

 that a set of rays conveying heat should all at ouce, in a certain 

 part of the spectrum, begin to give a small degree of light ; that 

 this newly acquired j)ower of illumination should increase while 

 the power of heating is on the decline ; that when the illuminating 

 principle is come to a maximum it should in its turn also decline 

 very raijidly and vanish at the same time with the power of heating. 

 How can effects that are so opposite be ascribed to the same cause ? " 



509 Relation of the refraugibility of the maximum heat-making rays 



and that of the rays of maximum luminousity. 

 Table I. — Containing the results of experiments 24 to 30. 



510 Table II. — Containing the results of experiments 31 to 43, followed 



by a discussion of the same. 



511 Table III. — Results of experiments on liquids. 



511 Table IV. Containing the stoppages occasioned by scattering sub- 

 stances. 



512-519 Argument founded upon the data contained in these four tables. 

 The general course of this argument is that, assuming the heat- 

 making rays and rays of light to be of the same nature, a ratio of 

 the efficacy' of the invisible rays to that of the luminous rays de- 

 rived from one set of experiments is incompatible with the ratio 

 derived from any other set. Under the assumption that the heat- 

 making rays are essentially different from light rays, this incom- 

 patibility does not appear. 



520 Table V. Stoppage of Prismatic Heat of the BefrangibiUty of the Bed 

 Bays, and of the Invisible Bays. 

 [The measurements on dark-red glass here quoted is Herschel's de- 

 cisive experiment, proving that heat-making rays are not the same 

 by nature as the light rays. The experiment involves a i^hotome- 

 tric determination not described, the result of which is, however, 

 quoted.] 



521-523 Argument founded upon data in above table. 



524 Table VI. Containing the results of the experiments on the trans- 

 mission of terrestrial heat. 



525-527 Showing the impossibility of explaining these results by any as- 

 sumption as to the ratio of the eflicacy of visible and invisible rays. 



528 Table of the Transmission of Terrestrial Scattered Light through various 

 Substances; with a short Account of the Method by ivhich the Besults 

 contained in this Table have been obtained. 



528-531 Description of the method and apparatus used, both being founded 

 upon the principles of Bouguer. The sources of scattered light 

 were vanes of white paper illuminated by a lamp. 



532-533 Table VII. This table contains the transmitting power for light 

 of nearly all the substances used in the experiments of this paper. 



533 Table of the Propoiiionul Terrestrial Light Scattered by various S-ub- 

 stances. 



