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 XXXII. Intelligence and Miscellaneous Articles. 



ON A DEW-BOW SEEN ON THE SURFACE OF MUD. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 SPHERE was seen today (February 13, 1862) by myself and some 

 ■*■ other persons in this neighbourhood, a very beautiful phenomenon, 

 of which the cause is obvious, and of such a nature that one would 

 expect the phenomenon to occur frequently ; but I do not remember 

 to have yet seen any instance of it recorded in any scientific publi- 

 cation. I refer to a prismatically-coloured hyperbolic iris, or bow 

 of the first order, exactly resembling that sometimes seen on a field 

 of dewy grass ; but in this case it was displayed on the muddy sur- 

 face of a by-road near Glasgow, and on the less trodden parts of 

 an adjoining turnpike road, throughout a distance of more than a 

 mile. The time was between 12 h 30 m and l h p.m. Greenwich time ; 

 the morning had been hazy, but the mist had cleared away, and the 

 sun was shining brightly. 



The angular dimensions of the iris were obviously the same with 

 those of a rainbow of the first order ; its colours were complete, 

 from red to violet, and very bright and distinct, especially where the 

 mud was softest and moistest ; where a sheet of water, how thin 

 soever, covered the mud, the iris vanished. No trace of an iris 

 could be seen on the grass, in the sky, or anywhere but on the mud ; 

 and on those parts of the turnpike road where the mud had been 

 much disturbed no iris was visible. 



The necessary conclusion from this appearance is, that the sur- 

 face of the mud must have been thickly covered with globules of pure 

 water, perfectly spherical, and not in absolute contact with the mud, 

 although resting on it ; but those globules must have been extremely 

 minute, for they were invisible to the closest inspection with the 

 naked eye. 



I am, Gentlemen, 



Your most obedient Servant, 



Glasgow, February 6, 1862. W. J. Macquorn Rankine. 



NOTE ON THE THEORY OF SPHERICAL CONDENSERS. 

 BY M. J. M. GAUGAIN. 



I have indicated in my preceding communications* a general 

 principle by means of which all questions relative to condensers may 

 be transformed into questions of propagation, and thus brought 

 within the domain of Ohm's law. The exactitude of this principle 

 has been already demonstrated experimentally, — 1, in the case of 

 concentric cylindrical condensers ; 2, in the Case of eccentric cylin- 

 drical condensers ; 3, in the case of plane condensers (Comptes 

 Rendus, Feb. 18, April 29, and June 17, 1861). I have now verified 

 * See Phil. Mag. vol. xxi. p. 539. 



