72[1265] that, owing to evaporation and
other changes produced by rapid approach to the sun, electrical
processes of considerable intensity must take place in comets; and that
their original light is immediately connected with these, and depends
upon solar radiation, rather through its direct or indirect electrifying
effects, than through its more obvious thermal power, may be considered
a truth permanently acquired to science.[1266] They are not, it thus
seems, bodies incandescent through heat, but glowing by electricity; and
this is compatible, under certain circumstances, with a relatively low
temperature.

The gaseous spectrum of comets is accompanied, in varying degrees, by a
continuous spectrum. This is usually derived most strongly from the
nucleus, but extends, more or less, to the nebulous appendages. In part,
it is certainly due to reflected sunlight; in part, most likely, to the
ignition of minute solid particles.

FOOTNOTES:

[Footnote 1188: _Month. Not._, vol. xix., p. 27.]

[Footnote 1189: _Mem. de l'Ac. Imp._, t. ii., 1859, p. 46.]

[Footnote 1190: _Harvard Annals_, vol. iii., p. 368.]

[Footnote 1191: _Ibid._, p. 371.]

[Footnote 1192: _Month. Not._, vol. xxii., p. 306.]

[Footnote 1193: Stothard in _Ibid._, vol. xxi., p. 243.]

[Footnote 1194: _Intell. Observer_, vol. i., p. 65.]

[Footnote 1195: _Comptes Rendus_, t. lxi., p. 953.]

[Footnote 1196: _Smiths. Report_, 1881 (Holden); _Nature_, vol. xxv., p.
94; _Observatory_, vol. xxi., p. 378 (W. T. Lynn).]

[Footnote 1197: _Ueber den Ursprung der von Pallas gefundenen
Eisenmassen_, p. 24.]

[Footnote 1198: Arago, _Annuaire_, 1836, p. 294.]

[Footnote 1199: Humboldt had noticed the emanation of the shooting stars
of 1799 from a single point, or "radiant," as Greg long afterwards
termed it; but no reasoning was founded on the observation.]

[Footnote 1200: _Am. Journ. of Sc._, vol. xxvi., p. 132.]

[Footnote 1201: _Annuaire_, 1836, p. 297.]

[Footnote 1202: _Ann. de l'Observ._, Bruxelles, 1839, p. 248.]

[Footnote 1203: _Ibid._, 1837, p. 272.]

[Footnote 1204: _Astr. Nach._, Nos. 385, 390.]

[Footnote 1205: _Am. Jour. of Sc._, vol. xxxviii. (2nd ser.), p. 377.]

[Footnote 1206: _Ibid._, vol. xxxviii., p. 61.]

[Footnote 1207: _Month. Not._, vol. xxvii., p. 247.]

[Footnote 1208: _Am. Jour. of Sc._, vol. xliii. (2nd ser.), p. 87.]

[Footnote 1209: Grant, _Month. Not._, vol. xxvii., p. 29.]

[Footnote 1210: P. Smyth, _Ibid._,