54 



NATURE 



{May 17, 1883 



Suchuoi, in the same latitude and in a very similar situation as 

 Cannes, in March, 1874, a year with a considerable number of 

 sunspots, there were three days which were more than 27 

 colder than the average, while in March, 1S83, with little or no 

 sunspots, the coldest days mentioned by Mr. Williams at 

 Cannes was only I7°3 colder than the average. 



I want only to show by this example that if it is wished to 

 prove anything a< to the varying inten-ity of the sun's rays, a 

 large number of observations in distant countries should be 

 given, especially in middle latitude;, the work of Dove having 

 well proved that there is always a compensation to a certain 

 extent between cold and warm areas, and a very great number 

 of these deviations being certainly due to causes which have 

 nothing to do with anything beyond the earth's atmosphere. 



St. Petersburg, April 17 A. Woeikof 



Sheet Lightning 



Looking to the south and south-east from the Bel Alp, the 

 play of silent lightning among the clouds and mountains is some- 

 times very wonderful. It may be seen palpitating for hours, 

 with a barely appreciable interval between the thrills. Most of 

 those who see it regard it as lightning without thunder — Blitz 

 ohm Donner, Wetterleuchten, I have heard it named by German 

 visitors. 



The Monte Generoso, overlooking the Lake of Lugano, is 

 about fifty miles from the Bel Alp as the crow flies. The two 

 points are connected by telegraph ; and frequently when the 

 Wetterlmchten, as seen from the Bel Alp, was in full play I 

 have telegraphed to the proprietor of the Monte Generoso Hotel, 

 and learnt in every instance that our silent lightning coexisted in 

 time with a thunderstorm more or less " terrific " in Upper 

 Italy. John Tyndall 



May 12 



I AM glad to find that M. Antoine d'Abbadie's remarks con- 

 firm in the main those which I have made on the above subject 

 in Nature (vol. xxviii. p. 4), especially as to the occurrence of 

 lightning at a great altitude as observed in low latitudes. 



In stating that he has frequently observed " thunder without 

 lightning, and lightning without thunder," does M. d'Abbadie 

 mean that, like every one else, he has observed thunder without 

 observing lightning, and lightning without observing thunder ? 

 Or have we here a living advocate not only of the dumb light- 

 ning, but of the dark (lightningless) thunder? 



The thin and local fogs which are not uncommon in thundery 

 weather readily transmit the illumination of a distant flash of 

 lightning. It seems highly probable that in such cases the 

 lightning may be occasionally supposed to be an electric dis- 

 charge occurring in the fog itself, just as a flickering aurora 

 seen above thin clouds has ofien been supposed to have its 

 habitat in the clouds themselves. 



The suggestion of M. d'Abbadie is a fair one, and I for my 

 part shall be glad to undertake observations uf "sheet lightning " 

 this summer in conjunction with any one resident about forty 

 miles from this place, the observers interchanging reports by the 

 earliest post after the hour of observation. 



W. Clement Ley 



Ashby Parva, Lutterworth, Leicestershire 



[The objection of your correspondent is valid. I am informed 

 independently and by high authority that the velocity of sound 

 in hydrogen must be considered as barely fourfold greater 

 than in air, the number of vibrations per second emitted by a 

 hydrogen whistle being increased in the same proportion. 



In making my earlier estimate I had been misled by an 

 erroneous statement in a work that is still of much general 

 credit and authority, to which I referred for ascertaining the 

 velocity of sound in different gases, as it happened to be the 

 book then nearest at hand, and as I have no special knowledge 

 of the subject. It was the first edition of the Penny Cyclopadia, 

 where in the article " Acoustics," p. 95, I lit upon the following 

 passage, which professed to give the precise information I 

 wanted: — "Thus air being about thirteen times as heavy as 

 hydrogen, the velocity of propagation in the latter is about 

 thirteen times that in the former." I need not take up your 

 space by quoting the paragraphs before and after this, which 

 emphasise and corroborate the statement and make it clear that 

 it was no slip of the pen. Possessors of this Cyclopaedia (I know 

 nothing of subsequent editions) would do well to look out the 

 passage and put a note of warning by the side of it. 



The fourfold gain, or nearly so, of the hydrogen whistle is 

 not to be despised. It is sufficient to establish its rank as the 

 emitter of the largest number of aerial vibrations per second of 

 any instrument yet contrived. My little whistle, of about 1 mm. 

 bore, require; a very small supply of air, a bag that I fill with a 

 single expiration containing enough to keep it in continuous 

 sound for many minutes. As yet I have not got a portable 

 holder for pure, dry hydrogen, but a well-known chemist is 

 kindly making an experiment of one for me. 



Francis Galton] 



Hydrogen Whistles 



In his interesting communication on the above topic (Nature, 

 vol. xxvii. p. 491) Dr. Francis Galton has inadvertently fallen 

 into a mistake which quite seriously affe-ts the numerical deduc- 

 tions which follow. He erroneously assumes that " the number 

 of vibrations per second caused by whistles is inversely propor- 

 tional to the specific gravity of the gas that is blown through 

 them." 



It is well known that the number of vibrations is inversely 

 proportional to the si/uart root of the density or specific gravity 

 of the gas. Hence for hydrogen, as compared with air, the 

 number of vibrations per second produced by a given whistle 

 would be increased only about 3 '6-fold instead of 13-fold, as he 

 estimates it. Similarly the number of vibrations by the use of 

 hydrogen in the little whistle when set at 0^14 inches would be 

 only about 86,533, instead of 312,000. John Le Conte 



Berkeley, Cal., April 12 



The Pillar of Light 



I have frequently observed this phenomenon. The first time 

 I saw it was on April S, 1S52, when I saw it here at sunset, and 

 on April ill saw it at sunrise when I was in the Irish Channel, 

 near to Port Patrick, where I was laying a submarine cable. 



In the Monthly Notices of the R.A.S. vol. xii. p. 185, there 

 are several notices of its having been seen at that time in various 

 places. I saw it last on April 6 this year, when it had the same 

 appearance as previously, which is well represented by Mr. 

 Symond's drawing on p. 7, except that the 1 >wer part is too 

 bright, and it looks more correct when shaded with a pencil. 

 The pillar is always perpendicular to the horizon and to the 

 sun's position. I saw the zodiacal light several times in 

 February, extending as far as the Pleiades, and at an angle of 

 about 45 . I think it is highly probable that the pillar of light 

 is caused by reflection from ice crystals, as we had very cold 

 weather early in April, and have still. These atmospheric phe- 

 nomena are often best seen reflected from a plate gla-s window. 



Gateshead, May 9 R. S. Newall 



Remarkable Lunar Phenomenon observed at Weston- 

 super-Mare, August 21, 1861 



At about 8.30 p.m. a band of silvery light appeared pro- 

 ceeding from the lower margin of the moon, in a line perpen- 

 dicular to the horizon. The width of this band was eqnal to 

 the exact apparent diameter of the moon's disk. Slowly the 

 band lengthened, until its upper portion reached beyond the 

 moon to the extent of about two diameter-, while the lower 

 limb extended itself to about the length of four diameters, 

 where its foot rested apparently on a light fleecy cloud. In a 

 few minutes a similar band traversed the other at right angles, 

 forming a perfect Latin cross, the brilliant face of the moon 

 occupying the place of intersection. The arms of the cross 

 were respectively about two diameters of the moon's face. 

 The portion of the sky in which this occurred was clear, but 

 clouds were slowly drifting from the west, and in ten minutes 

 began to obscure this beautiful and unusual phenomenon. 



The only record of any similar phenomenon which I can 

 meet with is to be found in Lowe's treatise on atmospheric 

 phenomena, wherein two in-tances are described. The observer 

 of one was Dr. Armstrong, and the appearance was seen by 

 him at South Lambeth on February 25, 1842. The other ob- 

 server was Mr. Lowe himself, who was at Derby railway station 

 when the phenomenon occurred. In both these instances, how- 

 ever, the crossbeam was absent. Although no hypothesis has 

 been suggested to account for this appearance, it may be inter- 

 esting to note that in the case recorded by Mr. Lowe, the very 



