304 



NATURE 



\Fcb. 15, 1872 



and with mountains on every side, the tnie horizon was not 

 visible, and it was impossible to make very accurate observations. 

 The rosy clouds remained long after the coruscations had died 

 away, but the chief splendour was displayed for an hour and a 

 half after sunret. 



If the aurora of this spring was not more brilliant than those 

 of the last two autumns, it was, I think, more remarkable for its 

 sharp contrasts of colour, and for the peculiar " coal-sacks," or 

 areas of blackness, which seemed to be actually a part of the 

 aurora as much as the red or green light. 



David Wedderburn 



I IIA^E to correct an important error in my account of the 

 aurora of the 4th, published by you on the 8th. I stated that 

 it was finest between 6 and 7. At 9 it appeared to be fading, 

 and 1 ceased to watch it ; but I learned afterwards that it re- 

 kindled, and was at its highest between 9 and 10. The colour 

 was still red, and the columns of light met near the zenith. 



Joseph John MuRrHY 



Old Forge, Dunmurry, Co. Antrim, Feb. :2 



The Great Comet of i85i 



The following observation may interest your readers. It is 

 taken from a volume entitled, " The Industrial Progress of New 

 South Wales," published by authority of the Colonial Govern- 

 ment. Under tlie head of Astronomical Progress is a paper by 

 Mr. Tebbutt, in which he says that, while observing in Australia 

 on the morning of July i, iS5l {i.e., really, in the afternoon 

 before sunset of our June 30), he noticed the widening out of 

 the branches of the tail of the comet then visible. He remarks 

 that this obs!:rvation is very interesting when taken in connection 

 with the announcement made by Mr. Hind, that "it appeari not 

 only possible, but even probable, that in the course ot June 30, 

 iSfil, the earth passed through the t.-.il of the comet, atadistance 

 of perhaps two thirds of iis length from the nucleus." 



There were at least two observers in England of what was 

 probably the opposite effect of perspective (viz., tlie closing up 

 of the branches of the tail) on the evening of June 30. The 

 i-apid, angular motion cf one of the streamers was separately 

 observed by Mr. George Williams, of Liverpool, and the Rev. 

 T. W. Webb, of Ilardwick, the latter of whom has given a de- 

 tailed account of his observations in the " Monthly Notices of the 

 Royal Astronomical Society," voL xxii., p. 311. According to 

 these observations, our actual passage through the streamers of 

 the tail must have taken place about sunset on the evening of 

 June 30. A. C. Ranyard 



ON LUMINOUS MATTER IN THE ATMO- 

 SPHERE 



MUCH has lately been written and lectured on atoms, 

 molecules, organic niattor suspended in the air, 

 effects of the light passing through the sky, abstracting 

 its blue colour, and changing it into red. May I there- 

 fore be allowed to add some facts which I noticed during 

 a long and careful observation of a hitherto almost un- 

 known phenomenon to which my attention was drawn by 

 chance. 



Some years ago I had directed my excellent six-feet of 

 Merz, Munich, towards the sun in order to draw the 

 sun-spots in the camera- obscura. One day (April 27, 

 1863), when the sun had scarcely passed, and I was push- 

 ing the instrument to get its disc again in the field, I 

 was astonished to perceive a mass of luminous little 

 bodies, apparently coming from the sun, and passing 

 altogether with great velocity towards the east. They 

 brightened in a white and sparkling light, and were as 

 numerous as stars ; but as their velocity was much too 

 great, and as they disappeared when I followed them to 

 some distance from the sun, I was inclined to take them for 

 little bodies floating in the atmosphere, and getting their 

 light from the sun, an opinion which soon became 

 stronger when I grew aware that I had to draw out the 

 eye-piece some millimetres in order to get them quite clear 



and distinct. As I had never heard of the existence of any 

 such bodies, I resolved to give notice to Dr. Wolf, 

 Director of the Observa'ory at Zurich, who convinced 

 himself of the strange phenomenon, and, encouraging 

 me to persist in my investigations, told me that the late 

 Sig. Capocci, on the Capodimonte Observatory at 

 Naples, had mentioned these little bodies appearing to 

 him under similar circumstances on May 11, 1845. 

 Since that time Prof. Dr. Edward Heis, of Miinster, West- 

 phalia, in his " Wochenschrift fur Astronomie," 1869, 

 March 24, also gave full corroboration to this fact. I there- 

 fore went on, and uniting the investigation to the daily 

 labour of observing and drawing the sun spots, my arrange- 

 ment of the camera-obscura improved and ensured these 

 results as well. Convinced of the importance of the 

 phenomenon, I resolved to direct my whole attention to it, 

 and to examine it thoroughly. I decided to find out not 

 only the distance, the size, the shape, the frequency, the 

 velocity, and the nature of the light of these little bodies, 

 butalso to take notice of their daily direction by comparing 

 it with the simitltaneous direction of winds and clouds. I 

 continued my observations during a period of three years. 

 As I mentioned above, I was obliged to draw out the 

 eye-piece of the telescope in order to have the little 

 objects more distinct. Now, everybody knows that the 

 focal distance of any lens, or system of lenses, such as the 

 telescope is, will dift'er according to whether the beams 

 come iVom a more or less distant object. The little 

 bodies did not appear distinct in the focus of the sun ; I 

 had to draw out the eye-piece ; but if the focal distance 

 was greater, their distance was smaller than that of the 

 sun, and by means of a scile placed on the eye-piece, I 

 soon obtained the result that these little bodies belong to 

 our atmosphere, floating in a stratum of about 4,000 metres 

 down to about 200 metres, the moit numerous swariii pass- 

 ing almost always at a distance of not less than 500 metres. 

 Here I remark that fur my observations 1 had chosen the 

 time of the sun being in, or about, the meridian, for then 

 I was sui'e to have its light as strong, and the sky as clear 

 as possible, while mostly preferring a magnifying power 

 of only 48 diameters. 



Taking the little bodies in the right focus, I was enabled 

 not only to draw their shape, which I found very various, 

 but also to measure their apparent diameter', which did 

 not differ less, and depended much on distance, the nearer 

 ones being larger, and, as I learned from the scale the 

 accurate distance of every one, I calculated their diameter 

 to vary from 10 to 59 millimetres, the average being 32 

 millimetres. Their shape was very various, too. The 

 greater number were oblong, angular, resembling flakes, 

 sonre few wcr'e orbicular, while some smaller ones were 

 star-shaped, with transparent arms. 



With respect to their frequency, I was surprised to find 

 on certain days,especiallyinApril andMay, an incalculable 

 number of little bodies in the field of the instrument, 

 passing without interruption for hours. In general I found 

 their number to be connected with the purity of the sky ; 

 and every day I noticed the average, the daily minimum 

 occurring in the morning and evening hours, the maximum 

 in the noon-tide hours ; also the annual minimums in the 

 summer and winter months, the chief maximum from 

 April 20th to May 15 th, the second, much lower maximum 

 in August and September. I often saw their number in- 

 crease soon after clouds had passed. 



The velocity of the bodies, irregular in the lower strata, 

 being about 2 metres in a second, became greater and 

 more regular in the higher ones, where, for instance, at a 

 distance of 3,000 metres, I found them to pass 8 metres 

 during the same period, a rapidity agreeing closely with that 

 of the cirri, which often passed at or above this distance. 

 Whether far or ne.ir, all tliese little bodies glittered in a 

 magnificent white light behind the sky, but as it retreated 

 farther from the sun its blue colour became darker, 

 the light of the bodies consequently diminished, and was 



