1818-3 Scientific Intelligence. 235 



wash by surrounding my still with water of the temperature of 

 160°. Now this operation could not be effected in a common 

 still by surrounding it with water of the temperature of 212° ; nor 

 could the ebullition in the common still, if produced by other 

 means, be maintained by the heat of 212° in the surrounding 

 water. It appears then that a lower heat suffices to commence 

 distillation in vacuo, and that a less heat suffices to maintain 

 the operation when begun ; of course there is a less expenditure 

 of fuel. I shall be obliged by the insertion of this letter in your 

 next number ; and 1 am, Gentlemen, 



Your obedient servant, 



Henry Tritton. 



XI. Parhelion and Parhelia, seen at Gosport, Aug. 26, 1818. 

 By William Burney, Esq. LL.D 



At half-past six, a. m. a fine parhelion appeared on a thin 

 vapour passing to a Cirrostratns cloud; it was situated E. by 

 N., and its altitude from the horizon, allowing for the necessary 

 corrections, was 15°; its distance from the true sun, which bore 

 E. by S. by the compass, was 22° 30" ; and its continuance 

 upwards of half an hour. No halo round the sun was perceptible 

 at the time. 



At half-past seven, a beautifully coloured parhelia appeared 

 on an attenuated Cirrostratns; namely, one on each side of, 

 and both horizontal with, and equidistant from, the real sun, 

 which was then 22° in altitude. These two mock-suns some- 

 times appeared at the same time for two or three minutes, and 

 at other times alternately, when their colours were brightest: 

 they disappeared twice from the intervention of clouds ; and, at 

 the place of their re-appearance, a bright light was first perceived 

 in the cloud, gradually forming into the shape of a cone lying 

 horizontally with its apex turned from the sun ; and at the base 

 of this cone, nearest the sun, there was a light red, a delicate 

 yellow, and lastly a pale blue, which altogether formed the mock- 

 sun : when the parhelia appeared most perfect, they were 

 circular, of an orange colour, and nearly as large again as the 

 apparent size of the sun's disc : only two parts of the solar halo 

 in which they were situated could be traced ; and these were 

 perpendicular through the phenomena, which did not disappear 

 till after eight o'clock. 



The State of the Clouds and Instruments. — During this rare and 

 pleasing sight, there were, in the vicinity of the sun, Cirrocu- 

 inuli and plumose Cirri descending to Cirrostrati, and Cumulus 

 clouds rising in the W. from whence a fresh breeze and vapour 

 sprang up. The barometer at 30 inches, but sinking slowly ; 

 the thermometer rose from 5b'° to 62° ; and De Luc's whalebone 

 hygrometer receded from 65° to 60°. Before 10 o'clock,, the 

 azure sky was completely veiled with compound modifications of 

 clouds, followed by large passing Nimbi and a few drops of rain. 



