462 Professor Tyndall [Jan. 18, 



calculated to suggest a notion prevalent on the Continent, that the 

 particles of a fog, instead of being full droplets, are really little 

 bladders or vesicles. Clouds are supposed to owe their power of 

 flotation to this cause. This vesicular theory never struck root in 

 England ; nor has it, I apprehend, any foundation in fact. 



As I stood in the midst of these eddying specks, so visible to the 

 eye, yet so small and light as to be perfectly impalpable to the skin 

 both of hands and face, I remarked, " These particles must surely 

 yield a bow of some kind." Tumiug my back to the sun, I stooped 

 down so as to keep well within the layer of particles, which I sup- 

 posed to be a shallow one, and, looking towards the " Devil's Punch 

 Bowl," saw the anticipated phenomenon. A bow without colour 

 spanned the Punch Bowl, and, though white and pale, was well 

 defined, and exhibited an aspect of weird grandeur. Once or twice 

 I fancied a faint ruddiness could bo discerned on its outer boundary. 

 The stooping was not necessary, and as we walked along the new 

 Portsmouth road, with the Punch Bowl to our left, the white arch 

 marched along with us. At a certain point we ascended to the old 

 Portsmouth road, whence with a flat space of very darlt heather in 

 the foreground, wo watched the bow. The sun had then become 

 strong, and the sky above us blue, nothing which could in any proper 

 sense be called rain existing at the time in the atmosphere. Suddenly 

 my companion exclaimed, " I see the whole circle meeting at my feet ! " 

 At the same moment the circle became visible to me also. It was the 

 darkness of our immediate foreground that enabled us to see the 

 lower half of the pale luminous band projected against it. We walked 

 round Hind Head Common with the bow almost always in view. Its 

 crown sometimes disappeared, showing that the minute globules 

 which produced it did not extend to any great height in the atmo- 

 sj)here. In such cases, two shining buttresses were left behind, which, 

 had not the bow been previously seen, would have lacked all signifi- 

 cance. In some of the combes, or valleys, where the floating particles 

 had collected in greater numbers, the end of the bow plunging into 

 the combe emitted a light of more than the usual brightness. During 

 our walk, the bow was broken and re-formed several times ; and, 

 had it not been for our previous exi)erience, both in the Alps and at 

 Hind Head, it might well have escaped attention. What this white 

 bow lost in beauty and intensity, as compared with the ordinary 

 coloured bow, was more than atoned for by its weirdness and its 

 novelty to both observers. 



The white rainbow (Varc-en-ciel hlanc) was first described by the 

 Spaniard Don Antonio de Ulloa, Lieutenant of the Company of 

 Gentleman Guards of the Marine. By order of the King of Spain, 

 Don Jorge Juan and Ulloa made an expedition to South America, an 

 account of which is given in two amply-illustrated quarto volumes to 

 be found in the library of the Royal Institution. The bow was 

 observed from the summit of the mountain Pambamarca, in Peru. 

 The angle subtended by its radius was '6'6'^ 30', which is considerably 

 less than the angle subtended by the radius of the ordinary bow. 



