544 



NATURE 



{Oct. 3, 1889 



remote from that to which the top has fallen " (see my former 

 letter). If this is the case, it would be strong proof that the 

 explosion actually took place in the core. I shall probably 

 have no opportunity of visiting the spot again for many months. 



My recollection is that there are no trees within several feet 

 of the line joining the two damaged ones, which stood in what 

 now looks like an opening in the wood. Mr. Pickering can 

 perhaps check this also. A. F. Griffith. 



15 Buckingham Place, Brighton. 



In several letters lately published in Ivature, an explosion 

 in or by a tree trunk is mentioned. Such an explosion occurred 

 here during the great storm of July 12 last. The lightning 

 struck an old crab-tree, at the base of the trunk, and exactly at 

 the ground-line. The crab was growing on the top of a grassy 

 bank. The lightning tore the bank open from top to bottom, 

 tore open and splintered the roots of the crab, and threw pieces 

 of roots and turf, all in one direction, for 21 feet ; the turf was in 

 large pieces, of about a foot cube. 



A tiled barn near here was, at the same time, struck in a 

 peculiar manner. The lightning struck the upper tiles near a 

 gable ; one tile was torn out and hurled away, and several other 

 tiles were neatly perforated with round holes, each about \ inch 

 in diameter ; the tiles were red, and the holes were burnt grey 

 all round. The wooden pegs belonging to the perforated tiles 

 were blackened by the heat, W. G. S. 



Dunstable. 



On the Remarkable Form of Hailstones. 



With reference to the description given in Nature (vol. xl. 

 pp. 151 and 272) of the hailstorm at Liverpool, it will probably 

 be interesting to bring under notice an early account of the 

 remarkable forms often possessed by hailstones ; it is to be found 

 in the Edinburgh Philosophical Journal for 1824, vol. xi. p. 326. 

 The writer of the said article states that " in the second part of 

 the eleventh volume of the ' Nova Acta Physico-Medica Acade- 

 miae Csesarese Leopoldinae Carolinse Naturae Curiosorum,' Dr. 

 Nogeralh informs us, that, on May 7, 1822, a tremendous hail- 

 shower fell in and around Bonn. . . . The general size of the 

 hailstones was about one inch and a half in diameter, with a 

 weight of nearly 300 grains. When whole, which was not 

 generally the case, the general outline was elliptical or com- 

 pressed globular, and the form cerebral, or resembling the brain 

 of a warm-blooded animal. . . . More frequently the form was 

 lenticular, and appeared polished on the two ends, as if by 

 friction. The masses had a concentric lamellar structure ; in 

 the centre was a white, nearly opaque, nucleus, of a round or 

 elliptical form, around which were arranged concentric layers, 

 which increased in translucency from the innermost to the outer- 

 most. They at the same time exhibited a beautiful stellular 

 fibrous arrangement, caused by rows of air-bubbles disposed in 

 radii. . . . Captain Delcross, in the thirteenth volume of the 

 ' Bibliotheque Universelle,' describes hailstones having the 

 concentric lamellar structure and stellular fibrous arrangement. 

 . . .The surface was provided with pyramidal forms. . . . When 

 the edges and the angles of the pyramids are melted down, the 

 cerebral form is produced ; when the masses of hail, having the 

 structures described, burst asunder, the fragments have a pyra- 

 midal form, and then forms what has been described under the 

 name of pyramidal hail." The writer then proceeds to describe 

 hailstones which fell on June 27, 1823, at Aberdeen. "They 

 (the hailstones) were included, almost universally, each by five 

 sides or surfaces, four plane, constituting the sides of an irregular 

 pyramid, and one spherical in place of a base. . . . The spherical 

 surface appeared, to the depth of one-twentieth or one-thirtieth 

 of an inch, to be solid as it was transparent. The rest of the 

 hailstone was opaque, consisting of crystals or minute columnar 

 forms, perpendicular to the spherical surface." Eight figures, 

 illustrative of the different kinds of hailstones, are given 

 (Plate ix.). 



Miss Holt refers to the metallic taste and the flavour of ozone 

 possessed by those which fell at Liverpool. The presence of 

 NH3 in hailstones was long ago established by Mene (Cotnples 

 rendus. May 19, 1851). J, Shearson Hyland. 



14 Hume Street, Dublin, 



Eritius hispanicus{l) on the Roman Wall. 



The accompanying note on this alien Scrophulariaceous plant 

 will, I think, be of interest to many of your readers, more espe- 

 cially to those who, as members of the British Association, took 

 part in the excursion on Thursday last from Newcastle to the 

 Roman Wall. 



The plant occurs on some Roman remains at Chesters, Chol- 

 lerford, Northumberland, the residence of Mr. John Clayton. 

 In the recent editions of Dr. Brace's " Hand-book to the Roman 

 Wall," it is named Eriniis hispanicus, but it appears to have 

 been previously known as E. alpinus. In endeavouring to 

 determine its authoritative name, I have ascertained that the 

 plant was called E. hispanicus by Persoon (" Synopsis "), who 

 regarded it as a doubtful species, whereas all other authors regard 

 it as a variety oi E. alpinus. There is a specimen, apparently 

 of this plant, in the Oxford Herbarium, collected by Endress 

 ("Plantas Pyrenaicae exsiccatae, Annis 1829-30 lectse ") which 

 he calls E. alpinus, var. lanuginosus ; Grenier and Godron 

 (" Flore Fran9aise ") call it E. alpinus, var. hirsuius ; Lange 

 calls it E. alpinus, var. villosus ; and Willkomm and Lange, in 

 their "Flora Hispanica," follow Grenier and Godron, giving 

 the other names as synonyms. It will doubtless be best to 

 accept Willkomm and Lange's conclusion, and adopt the name 

 E. alpinus, var. hirsutus, Grenier et Godron. 



I may add that £. alpinus, L., is mentioned, in Babington's 

 "Manual of British Botany," as occurring near Tanfield, in 

 Yorkshire, a locality which is also given in the last edition of 

 Hayward's "Botanist's Pocket-Book." However, in Arnold 

 Lees's "Flora of West Yorkshire" (1888), it is stated that this 

 plant has disappeared from Tanfield. Consequently Chesters 

 is now the only English locality for Erinus, and the only form 

 is the var. hirstctus. Sydney H. Vines. 



Oxford, September 23, 



Noctilucous Clouds, 



The recent communications in Nature in relation to ap- 

 parently self-luminous cloud-like bands in the skies after night- 

 fall, call to mind the analogous phenomena of noctilucous 

 clouds involving the whole visible firmament. 



We are indebted to the indefatigable industry and zeal of the 

 illustrious Arago for the collection of the scattered facts relating ■ 

 to the phenomena of self-luminous clouds of divers kinds. ^ 

 According to the records collected by him, noctilucous bands 

 and zones of clouds are sometimes associated with the electrical 

 manifestations accompanying distant thunderstorms. To this 

 class belong the luminous phenomena noticed by Rozier on 

 August 15, 1 78 1, and by Nicholson on July 30, 1797. In other 

 cases, the association of the phenomena with electrical disturb- 

 ances, is by no means obvious. To this class belong the 

 luminous clouds observed by Beccaria over his observatory 

 at Turin ; likewise the luminous appearances witnessed by 

 Deluc near London, and also those observed by Major Sabine 

 over the Isle of Skye in Scotland. In all these cases, the 

 noctilucous condition of the clouds was localized and confined 

 to bands or zones in limited portions of the sky. But under 

 certain conditions this apparently self-luminouS property of the 

 nocturnal clouds involves the entire visible hemisphere. It is 

 to this latter aspect of the noctilucous phenomena that I desire 

 to call attention. 



Omitting the consideration of the exceptionally rare and ano- 

 malous phenomena of so-called phosphorescent " dry-fogs," as those 

 of 1783 and 1831, in which the luminosity was so pronounced as to 

 enable one to read ordinary print at midnight, we come at once 

 to the generally recognized phenomenon of that faint diffused^ 

 cloud-luminosity which enables the "country doctor," witM 

 comparative security, to perform his lonely midnight drives onl 

 cloudy moonless nights. Frequently the glow is so faint that ita 

 is only possible to observe it at a distance from cities and large* 

 towns, in places where the air is free from smoke, and where- 

 the darkness of the sky is not affected by the general illumination 

 due to gas and electric lights. 



The conditions under which the phenomena most conspicuously 

 manifested themselves to my observations were during the 

 incipient stages of the autumnal north-east storms occurringf^ 



^ Annnaire dii Bureau des Longitudes pour V An\%-^7., pp. 246-50 ; ibid.Jk 

 1838, pp. 279-35. " CEjvres Completes de Arago," vol. iv. pp. 70-77. Arago'^ 

 "Meteorological Essays," translated by Sabln;, pp. 48-53 (London, 1855). 



