July i8, 1872] 



NATURE 



westerly station in Europe from which the phenomenon has been 

 observed with some approach to accuracy ; and if the centre of 

 the corona be, as it seems to be (pace some of your correspon- 

 dents), an actual, substantive point, and not merely the effect of 

 perspective, the following observations may help in determining 

 its height above the earth. At II. o exactly, Greenwich time, 

 tlie centre of the very well developed corona had an altitude of 

 6S", with an azimuth bearing of 21° E. of S., a little W. of mag- 

 netic S. (these measurements being taken as correctly as could 

 be done with a good-sized compass furnished with a clinometer), 

 and it was distant from a Lyne ( Vega) about 8" towards S.W. ; 

 this distance being afterwards diminished by the rotation of the 

 earth. The aurora was observed independently by Messrs. 

 Kinahan and Symes, of the Irish Geological ."Purvey, in the same 

 neighbourhood, and they also noted the proximity of the centre 

 to the above-mentioned star. I do not trouble you with other 

 details. M. H. Close 



Newtown Park, Black Rock, Dublin, July 13 



I WITNESSED last night what must have been a somewhat 

 brilliant display of aurora. From 10.45 ''•^'- '° '■■° ''■^' slight 

 breaks in the N. E. were brightly lit up with a rosy glare, and 

 another break in the X. with the green rays. Coruscations of 

 light Hashed up from time to time, and were visible even through 

 the clouds, which consisted of somewhat dense nimbus. The 

 display in a clearer sky must have been decidedly fine. 



Bridporl, Dorset, July 8 J. Edmund Clarke 



Registering Thermometer 



Mr. Whipple and Mr. Bushell have shown great ingenuity in 

 suggesting remedies for the copious condensation of moisture 

 which takes place in the interior of the jackets of minimum 

 thermometers on the grass. 



Both their suggestions I have found fail to work a permanent 

 cure ; the chloride of calcium (only of use when the stopping is 

 perfect) soon becomes super-saturated, and itself gives off 

 moisture. The putty and sealing-wax hold good for about five 

 or six months, and then the insidious moisture permeates again. 

 Would it not be better to adopt my very simple plan of discard- 

 ing the jacket altogether? It is absolutely useless, and no 

 stopping is really effectual in resisting for long the daily extremes 

 of heat and cold and damp and dryness these thermometers must 

 undergo. 



I have used a thermometer on the grass for the last three years 

 entirely unmounted, and find its indications in no way effected by 

 the loss of its outer coat. 



Charles H. Grii'fitii 



The Rectory, Stralfield Turgiss, Winchfield, Hants, 

 July 5 



Luminous Matter in the Atmosphere 



I WAS much interested by M. Waldner's short article on 

 " Luminous Matter in the Atmosphere " in the number of 

 N.\TURE for Feb. 15, 1S72. Being unable to see the particles 

 described, I applied to him for further directions, and he was 

 kind enough to inform me that they may be seen a vision dinrte 

 with a telescope. 



I have since found that many of the little bodies may be seen 

 with the naked eye by shutting out the powerful direct and late- 

 ral rays. This maybe done, e.g., by partly closing ihs jalousies 

 or outside shutters used here, and then looking for the particles 

 at about the distance of quarter of a degree, or of the sun's radius 

 from the border of his disc, when the sun is either just below the 

 upper edge of the shutter, or immediately above the ledge of the 

 house if it looks east and west. Shutters are not always neces- 

 sary. I have just seen great numbers by standing on the border 

 of the shadow thrown by the adjoining house. Even by hold- 

 ing my hat over my head I can perceive some of them. The 

 chief object to be aimed at is to prevent the eyes from being 

 dazzled by the direct rays of the sun. The same principle ex- 

 plains the reason why stars are sometimes seen during the day 

 from the bottom of a well or through a telescope, and why the 

 red iirotuberances of the sun become visible during an ordinary 

 or artificial eclipse. 



On the 9th and loth current, and again this morning, there 

 was a haziness round the sun, which gradually diminished as the 

 angular distance from his disc increased, until the sky became 

 beautifully blue at an angle of 25° or 30°. I found that the 



haziness was produced by the reflection of the sunbeams from 

 innumerable little particles. Many of them were distinctly 

 visible to the naked eye, but many more were seen with an 

 opera-glass or telescope. They passed too rapidly to be counted, 

 but fifty at least were in the field of my glass at one time. I 

 am sure that this is no optical delusion, for several of my friends 

 have seen them too. 



What were these little particles? M. Waldner supposes 

 them to be crystals of ice, and they certainly look like minia- 

 ture snowstorms. Perhaps some of your readers may be able to 

 decide whether the higher particles are composed of ice-like 

 cirri, the loftiest of the clouds. But some of the corpuscles of 

 the lower strata of the air are undoubtedly seeds, little organic 

 substances, insects, &c. I have caught several feathery little 

 seeds of this kind. They are almost imperceptible when seen 

 against some white substance, and are so light that the slightest 

 currents of air waft them to great distances. 



Another instance of numberless little vegetable substances 

 being blov\Ti here may be cited, namely, the pollen of the 

 pine trees growing on the Landes. An unusually large quan- 

 tity of this fell here on April 17, 18, 19, and 20, and may 

 probably be traced to three extensive fires of pine woods 

 sixty or eighty miles N.W. of Pau (April 14-16). The 

 pollen was doubtless drawn upwards by a strong current of 

 heated air, and then wafted to Pau by the wind, which 

 blew in the right direction (April 17-19). The wind 

 changed at Bordeaux on the 20th, and the pollen then fell 

 (April 21-22) near Perigueux, nearly as far to the N. E. of the 

 fires as Pau is to the S.E. A correspondent of the Times (April 

 30), mistaking the pollen for sulphur, announced that a shower 

 of this substance had fallen here, and supposed that it was con- 

 nected with the eruption of Vesuvius, which, however, did not 

 begin until the 24th. 



I would suggest that some record should be kept of the 

 direction of the wind which these particles indicate in different 

 strata of the atmosphere in fine weather. J. F. A.N'DERSON 



4, Place Duplace, Pau, June 12 



Vibration of Glasses containing Effervescing Liquids 



It is known that a glass containing effervescing liquid will not 

 give a clear note when struck, and that as the elfervescence sub- 

 sides the tone becomes more and more clear. When the liquid 

 is perfectly tranquil the glass will ring as usual, but on re-exciting 

 the effervescence the musical tone again disappears. Sir John 

 Herschel (Encyc. Met., Art. " .Sound "), who states that this 

 experiment appears to h.ive been originally made by Chladin, 

 quotes it as an "example of the stifling and obstruction of the 

 pulses propagated through a medium, from the effect of its non- 

 homogeneity ;" and, in explanation of the phenomena, he says : 

 — "We must consider what passes in the communication of 

 vibrations through the liquid from one side of the glass to the 

 other. The glass and contained liquid, to give a musical tone, 

 must vibrate regularly in unison as a system ; and it is clear, that 

 if any considerable part of a system be unsusceptible of regular 

 vibraiion, the whole must be so." 



The phenomenon, then, according to this explanation, is due 

 to the fact that the liquid, during effervescence, becomes non- 

 homogeneous, and thus obstructs the passage of the sonorous 

 vibrations from one side of the glass to the other. 



It is with much diffidence that I venture to express dissent 

 from so eminent an authority as Herschel ; but it does not 

 appear to me that the above explanation is entirely satisfactory, 

 for the following reasons : — 



1. It seems probable that the sonc^rous vibrations pass round 

 the glass rather than across it. For, if they pass across the glass, 

 that will occur whether it contains water or air. Vet the musical 

 tone of a glass containing air is not destroyed by suspending 

 within it, so as not to touch it, a ball or cylinder of wool or 

 cotton, although the sonorous vibrations certainly cannot pass 

 freely through that substance. 



2. If the non-homogeneity of the contained liquid be the 

 cause why the sonorous vibrations will not pass, whence comes 

 it that treacle, clear honey, &c., which are homogeneous fluids, 

 destroy the musical ring of a glass fully filled with any of them? 



The phenomenon presents itself to my mind as being due to a 

 certain amount of vibration communicated to the glass by the 

 agitation arising from the effervescence. This vibration — which 

 can be easily heard by placing the ear close to the glass — inter- 

 feres with that caused by striking the glass, and destroys more 



