I^eb. II, 1886] 



NATURE 



543 



this season, clear weather prevails, and thus there is much more 

 hope of good observations of the eclipse. As to pressure 

 observations, they would be most interesting at some distance 

 from the coast. A. WoElKOF 



St. Petersburg, January 24/February 5 



Parallel Roads 



The following, from an old note-boolc, may be of interest in 

 connection with this subject ; — 



I observed, in 18S1, the formation of parallel roads on a 

 small scale still in progress in a small plain about 3 miles long 

 and I broad, marl<ed in maps of Iceland as a lake, Sandkletta- 

 vatn (lat. 64° 21'). This was surrounded on three sides by 

 mountains, and the fourth was closed by a lava-stream. ^ The 

 plain is a perfect level of dark sandy mud without a vestige of 

 vegetation, and is evidently a shallow lake for the greater part 

 of the year. The shore is regularly terraced, the terraces being 

 2 or 3 feet apart. I thought at the time that the water must be 

 dammed back regularly during the winter to a certain height, 

 but that this height has diminished at three successive periods 

 owing to fresh channels being found through the lava at lower 

 elevations. In Goddalir there is a most instructive example of 

 the formation of river-terraces. Above the broad valley there 

 are two groups, over 1000 feet deep, terminating in a vast glacier 

 or ice-cap. These seem to have been filled in solid with moraine, 

 the remains of which still cling to the sides at all elevations. 

 The eastern one evidently became cleared out first, with the 

 result that an enormous mass of gravel was sjiread over the 

 whole width of the valley below. The western one next started 

 a torrent of its own, which cut down the level for some distance 

 on its own side to 30 or 40 feet lower. Finally, both torrents 

 united, and their greater transporting power again cut down the 

 level some 30 feet, with the result that there are now two level 

 terraces and the basis of a third. J. Starkie Gardner 



Colours in Clouds 



The coloured fringes to, and in, clouds I long ago found to be 

 very common, but I had no idea that there was any novelty, as 

 there would seem to be, in this fact. 



When tlie sun is setting behind a bank of clouds and there 

 are high cumulo-strati or strati, these will almost always, I believe, 

 be found coloured, at the proper distance from the sun, if viewed 

 through a suitable dark glass. The edges of the dark cloud will 

 often be so too. I believe these colours are always present ; 

 hidden by the brightness of the cloud which shows them, and the 

 glare of the lower air. The former is removed by the dark 

 glass, the latter by the interposition of the bank. 



The tint I believe depends on the density of the cloud 

 where it is formed. But it seems more probable that the 

 real cause is that the particles (of ice?) are larger and more 

 numerous where the cloud is more dense, and that, if their size 

 were increased independently of the density we should have 

 exceptional cases. 



I have seen these fringes to bright edges of dense cumulus, 

 but I must own that I never w.is quite satisfied that I was not 

 seeing two strata of cloud. The colours are very beautiful, and 

 often so strong that it is difficult to realise that the dark glass 

 has only removed a concealing glare. J. F. Tenn.\nt 



Ealing, January 29 



Movement of Telegraph-Wires 

 I HAVE frequently noticed the peculiar movement of telegraph- 

 wires noticed by your correspondent. For some time I took it 

 to be an ordinary case of vibration, but it presented .'■o many 

 peculiar features that I was induced to examine it more closely. 

 It frequently happens that when the temperature and dew-point 

 of the air are at or about the freezing-point, and the sky is clear, 

 the wires are chilled by radiation, and hoar-frost is deposited 

 upon them. With an almost imperceptible wind the hoar-frost 

 collects almost wholly upon one side of the wire in the form of a 

 wing, producing a torsional strain. The weight of the hoar- 

 frost, as compared with the weight of line, is so small that their 

 common centre of gravity is almost coincident with the centre of 

 the wire. When in this condition, if a light wind acts upon the 

 frozen wing, it imparts a reciprocating rotary motion to the 

 wire. Each time the vibration brings the plane of the protuber- 

 ance in a line with the eye, the wire almost disappears from 



sight, wliile when it is at right angles to that line it flashes 

 suddenly into view. If looked at from such a point that the 

 wing of hoar-frost moves backwards and forwards behind the 

 black wire, the effect is very much more marked. 



R. MOUNTFORD DeELEY 

 Mill Hill, Derby, February 2 



The Deltas of Glacial Rivers 

 An interesting fact connected with the Lake of Geneva has 

 recently been brought to light by M. Hornlimann, who is now 

 preparing a hydrographical chart of the Leman basin. From 

 the point where the Rhone enters the lake, to a distance of more 

 than 6 kilometres, the river-water, which is denser than the 

 lake-water, follows a trench in the alluvial deposits which 

 is from 500 to Soo metres wide, and which, even beyond St. 

 Gingolph, where the depth exceeds 2Co metres, is 10 metres 

 deep. .\ precisely similar groove has been observed at the 

 mouth of the Rhine in the Lake of Constance, with a depth of 

 70 metres and a width of 600 metres ; and similar though less 

 deep grooves are found opposite to the old mouths of the Rhone 

 and the Rhine in the two lakes. The greater density of the 

 river-water is owing to its lower temperature and to the vast 

 quantity of sediment suspended in it. The deltas of glacial 

 rivers flowing into lakes differ, then, in a remarkable manner 

 from the deltas of most rivers flowing into the sea ; the water of 

 these rivers, being less dense than that of the sea, spreads over 

 the surface, and thus helps to form bars. G. H. W. 



MAHWA FLOWERS 



ATTENTION has been publicly drawn of late to 

 " Mahwa Flowers" — the corollas o( Bassi'a latifolia 

 — as a cheap source of cane-sugar. This species of Bassia 

 is a tree attaining to a height of 40 to 60 feet, and 

 common in many parts of India, especially in Central 

 Hindustan. It has oblong leaves of firm te.\ture, from 

 5 to 6 inches long ; these fall in February, March, or 

 April, and are succeeded in March or April by the flowers. 

 These last for two or three weeks and then begin to fall. 

 The falls take place at night, and continue sometimes for 

 a fortnight. The fruits, which resemble a small apple, 

 ripen in three months ; the seeds, one to four in number, 

 yield an edible oil by pressure. It should be added that 

 the trees are self-sown, and that they flourish in very poor 

 and stony soil. 



When the Mahwa tree is in bud, the ground beneath 

 it is cleared of weeds, sometimes by burning. A single 

 tree may yield as much as six to eight maunds' of flowers ; 

 even thirty maunds have been asserted to have been col- 

 lected from one tree. These flowers have a luscious but 

 peculiar taste when fresh ; when dry they resemble in 

 flavour inferior figs. They form a very important addi- 

 tion to the food of the poorer classes in those districts 

 where the tree abounds, particularly in the neighbourhood 

 of woodlands and jungles. They are specially useful in 

 economising cereals in seasons of famine and drought. 

 They are sometimes eaten fresh, but more commonly sun- 

 dried, and are usually consumed with rice and the lesser 

 millets, or with seeds of various kinds, and leaves. It is 

 said that a man, his wife, and three children may be 

 supported for one month on two maunds of Mahwa 

 flowers.- 



It is not, however, as a direct article of food, nor as a 

 material for the preparation of a rough spirit by fermen- 

 tation (a very common use of these flowers) that Mahwa 

 blossoms are now recommended. It has been affirmed 

 that they may be employed as an abundant and very 

 cheap source of cane-sugar. In the Morning Post of 

 October 15, 18S5, appeared an article on this subject, in 

 which it was stated that, " If the Mahwa flowers be avail- 

 able in sufficient quantities for the sugar-makers of 

 Europe, there can be no question that the days of the 



* A Bengal maund equals 82^ lbs. av. irdupois. 



^ For an interesting account of the Mahwa tree and its products, see a paper 

 by E. Lockwood in the Journal of the Linnean Society ("Botany"), vol. 

 xvii. pp. E7-90. 



