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XLV. Notice of a colourless Atmospheric Arch seen in the 

 interior of Brazil. By William Jory Henwood, Esq., 

 F.R.S., F.G.S., Chief Commissioner of the Gongo Soco and 

 Bananal Gold Mines, tyc. tyc. 

 To Sir David Brewster, K.H., LL.D., F.R.S.L. % E., fyc. 



My dear Sir David, 



THE village of Cattas Altas is situated in long. 43° 15' west, 

 and lat. 19° 58' 30" south, on an open undulating expanse 

 of pasture land, about 3500 feet above the sea, bounded on 

 the south-west by the mountain-chain of the Caracas, which 

 rises from 4000 to 5000 feet above it, a deep narrow glen 

 intervening between them. 



At about seven o'clock in the morning of the 12th of May 

 last*, I had occasion to cross this open country towards the 

 north-west, almost on the edge of the ravine. A dense mist 

 covered all the lower grounds, whilst the little hills shone in 

 unclouded sun-light ; in the fog a light air from the westward 

 was perceptible, but a gentle breeze in an opposite direction 

 prevailed on the hills. 



During my journey I passed several times from sunshine 

 into mist, and vice versa. 



Whilst immersed in fog on the verge of the vale, and some 

 400 feet above its bottom, an arch of about forty-five degrees 

 in altitude became visible. In width, and indeed in every other 

 respect, it exactly resembled a rainbow, except that the whole 

 of its upper part was entirely colourless, being, as it were, a 

 bow of denser mist surrounded by the ordinary fog. For an 

 altitude of about ten degrees, however, of the lower portion, 

 which was beneath the horizon of my station, it had the faint- 

 est possible tint of violet colour, which was rather more per- 

 ceptible in the south-eastern extremity than in the other. 



On entering the mist a second time, a few minutes later, I 

 observed a similar, but fainter and less perfect arch. 



My isolated situation affords me access to but few books of 

 reference ; and as but one of these mentions a colourless rain- 

 bow f, and as I have never before seen one myself, I venture 

 to trouble you with this brief notice of a phaenomenon which 

 perhaps may not be of frequent occuirence. 

 I have the honour to remain, 

 My dear Sir David, 



Your most faithful, humble Servant, 



Gongo Soco Gold Mines, Brazil, W. J. Henwood. 



June 3, 1848. 



* At Gongo Soco, about sixteen miles off, the temperature at 6 a.m. was 

 51°, and at 9 a.m. 63°. 

 t Encyclop. Brit., 6th edit. (1823), article " rainbow." 



