Optics. — Electricity. 369 



zoic acid were formed similar to- those obtained in the usual way, but only 

 less regular. As the flash did not continue after each crystal was depo- 

 sited, M. Buchner thought that the light was produced by a neutralization 

 of electricity. M. Buchner observed similar phenomena in the crystalli- 

 zation of acetate of potash, and M. Dobereiner observed the same in the 

 preparation of oxygen by means of a mixture of oxygenated chlorate, pot- 

 ash and manganese in powder. The last of these chemists is of opinion, 

 that those salts which contain no water of crystallization, are particular- 

 ly powerful in producing light during crystallization. See Neue Journ. 

 fur Chem. und Phys. 1824, vol. ii. p. 222, and Giorn. de Fisica, vii. 470. 



8. Iridescence of Clouds. M. de Humboldt mentions this phenomenon 

 as having been seen by him in South America, but I have not met with any 

 notice of its having been seen in this country, though it has most likely been 

 witnessed by some of our meteorologists who are accustomed to observe the 

 nepheological phenomena. On the morning of the 13th of December last, 

 we had a bard gale from the N. W., with black and dense cumulostrati 

 driving rapidly in the direction of the wind. At 9^ a. m., when examin- 

 ing the appearance of the heavens through an opening in the cumulostrati, 

 I observed an extensive cirrostratus resting motionless in a higher region 

 of the atmosphere, stretching from S. E- to E., and rising about 5° above 

 the horizon, the sun at that time being about 7° or 8° high. This cirro- 

 stratus exhibited all the prismatic colours in broad alternate stripes. There 

 were four alternations, and the tints being very brilliant, it formed a most 

 beautiful spectacle. It lasted till 11 a. m., when the colours gradually 

 faded, and at last blended into a uniform yellowish brown- Since that 

 time I have frequently seen the same phenomenon shortly after sunrise, 

 when the rays of the sun are incident at small angles, upon a thin and 

 shallow cirrostratus. 



The cause of the iridescence is not easily explained, but it seems to be 

 connected with the magnitude of the aqueous globules of which the cloud 

 is composed. 



I may give another instance, which took place on the 21st of January 

 Wind brisk, from the W. by N., Hygrom- 3-5 ; an extensive black cloud 

 veiled the heavens, extending from N. E. and W. to within 10° of the 

 southern horizon. The sun's place was completely obscured ; but a small 

 portion of the south edge of the cloud had a dazzling yellow colour- At 

 this time a chain of scud, flying from S- to S. E., crossed in succession the 

 illuminated part, each, as it passed, suddenly displaying a splendid show 

 of prismatic tints, and then returning to its original sombre hue. I watch- 

 ed this interesting sight for ten minutes, when a nimbus approached, anil 

 effectually darkened all that part of the heavens. 



J. Foggo. 



ELECTRICITY. 



9. Remarkable Electricity of Oxalate of Lime.— Having obtained, by 

 precipitation, some oxalate of lime, and dried it when well worked in a 

 VOL. IIT. NO. II. OCTOBER 1825. a a 



