December 12, 1895] 



NATURE 



131 



Flight of Birds Across the Moon's Disc. 



On the evening of October 7, 1895, while observing the 

 passage of the moon through the Pleiades for occultations, my 

 •attention was attracted by a flight of birds across the moon's 

 disc. This continued with more or less regularity the whole 

 time I was at work, from 7.30 to 9.30, the birds usually crossing 

 singly, but sometimes in groups of two, three, or even four. In 

 all, I saw perhaps 50 or 60 ; assuming a like frequency during 

 the intervals when I was not at the telescope, from 200 to 250 

 must have crossed the disc during the two hours. All were 

 flying south with a single exception. Their outlines and the 

 flapping motions of their wings were very distinct ; none 

 were soaring. The telescope is a 1 2-inch refractor : eyepiece 

 of power 90. The moon was low, its altitude ranging from 

 5° to 15°. 



The time occupied in transit varied from four to eight seconds, 

 the difference in apparent size being very marked, and the larger 

 always taking the less time. Assuming a rate of twenty miles 

 an hour for their flight, the distance would be about 5 miles 

 for a bird making a transit in eight seconds, or 2^ miles 

 for four seconds. Taking into consideration the altitudes of the 

 moon when the above transits were timed, the corresponding 

 altitudes of the birds above sea-level ranged from 2700 to 5000 

 feet. Considerations as to its size make it probable that these 

 figures are none too small. It may be of interest to note that 

 the Observatory stands on a promontory jutting out about 5 

 miles from the general trend of the Syrian coast, and that 

 according to these calculations the birds were flying either just 

 along the coast-line or over the sea. 



I may add that, in addition to Mr. Bray's experience, given 

 in Nature, No 1348, several accounts of similar observations 

 are given in Newton's " Dictionary of Birds," with estimates of 

 altitudes, ranging, for the most part, much higher than those 

 given above. Robert H. West, 



Syrian Protestant College, Beirut, November 25. 



A Luminous Centipede. 



Returning home on a very dark evening a few days ago, I 

 ■saw on the ground a greenish phosphorescent light which, in the 

 <listance, I took to be a glowworm (Lampyris uoctiluca), but a 

 nearer approach showed a luminous thread-like wormjof \\ inches 

 in length, moving in curves along the gravel drive. I stooped 

 and placed a finger and thumb on either side of the glowing 

 thread without actually touching it, and in a few seconds 

 observed that, aware of danger either from scent or vibration, 

 the insect showed a remarkable power of control over its 

 luminosity, invaluable for protection. It began to extinguish its 

 light, and in a most peculiar fashion, not dying slowly out all 

 over, but with a rapid wave of darkness sweeping from the tail 

 to the head, then in a second or so glowing brightly all over 

 again, repeating the manoeuvre several times so long as my finger 

 and thumb remained in its vicinity. A glass was brought, into 

 which I transferred the insect, where it glowed with a lessened 

 light for three or four hours. The next night the phosphor- 

 ■escence was very feeble, and on the morning following the insect 

 was dead. 



Seen in the daylight my capture appeared to be a thin thread- 

 like centipede, orange coloured, furnished with a fringe of fine 

 hairs on either side of its many-segmented body. 



Rose Haig Thomas. 



The White House, Basildon, November 27. 



The above communication certainly refers to one of the 

 luminous centipedes of the family Geophilidte ; and since the 

 species that most commonly draws attention to itself in England 

 by the exhibition of phosphorescence is of a reddish-orange 

 colour and is known as Ltnotieiiia crassipes, there is no reason 

 to doubt that the specimen under discussion was an example of 

 this species. The property of luminosity lies in an adhesive 

 fluid secreted by glands which open upon the lower surface of 

 the body, and the power of discharging or retaining the fluid 

 appears to be entirely under the centipede's control. 



The phenomenon is observable during the autumn months, from 

 about the middle of September to the end of November, and 

 although its significance is not clearly understood, it is generally 

 believed to be connected with the pairing of the sexes. 



R. I. POCOCK. 



NO. 1363. VOL. 53] 



The Critical Temperature of Hydrogen. 



In the October number of the Proc. Phys. Soc, Mr. 

 "G. H. B. ," after quoting Wroblewski's paper "Die Zusam- 

 mendriickbarkeit des Wasserstoffes " (IVienerSihb., 1889), says 

 (referring to my paper " On the Critical Temperature of 

 Hydrogen," Bu/l. Acad. Cracovie, March 1895): " Natanson 

 does not appear to have made any fresh experiments on the 

 subject, and the conclusions arrived at in his paper are therefore 

 not results of independent original investigation." It is diflicult 

 to understand the right Mr. " G. II. B." has to ignore the pro- 

 fessedly theoretual character of my paper. To blame a writer 

 offering theoretical deductions on the account of his not having 

 made "fresh experiments," is surely a criticism of extraordinary 

 character. Wroblewski's critical data are not in the least the 

 outcome of direct experiment, but have been calculated from an 

 empirical equation, constructed to represent Wroblewski's com- 

 pressibility curves. My reasoning and calculation are utterly 

 different, being founded upon Van der Waals' law of thermo- 

 dynamic correspondence. Besides, there are other points in my 

 paper, and they have no relation with whatever Wroblewski has 

 written.' All this will be seen at once on comparing my paper 

 with that of Wroblewski's. But from Mr. G. H. B.'s own 

 words, it must be inferred that, before publishing what implies 

 a serious accusation, he did not take the trouble of looking 

 with his own eyes at Wroblewski's paper. 



Ladisi.as Natanson. 



Cracow University, November 28. 



A METEOR PHOTOGRAPH. 

 'T^HE accompanying photograph (p. 132) was obtained 

 -*■ on Saturday night, November 23, about I2h. 15m., 

 by Mr. C. P. Butler, at Knightsbridge. With the inten- 

 tion of focussing and testing the field of a new lens, he 

 had placed a quarter-plate camera on the window-sill, 

 pointed it roughly at the region near the boundaries of 

 Perseus, Andromeda, and Aries. He was necessarily in 

 darkness during the exposure, but uncovered the plate 

 about I2h. I cm., and terminated the exposure at I2h. 

 20m., so that the limits are close enough for recognising 

 the meteor if it chances to have been recorded elsewhere, 

 On developing the plate on the following Monday, the 

 track of the meteor was the first impression to be 

 perceived, and, not knowing of its occurrence during the 

 taking of the photograph, it was thought that the plate had 

 by some mishap been spoiled. Having finished develop-^ 

 ing, however, and after fixing, it was seen that this was 

 not the case, the strange appearance being evidently 

 an image of some meteor flashing past during the 

 exposure. The star trails (the camera was fixed, so the 

 stars are represented by short lines about an eighth of an 

 inch long) are all distinct, but owing to the region 

 included in the field being almost barren of bright stars, 

 with the exception of «, /3, and -y Arietis, which come in at 

 the edge of the plate, they are too minute to bear 

 reproduction. 



Confirmation of the occurrence of the meteor is given 

 by its having been observed from the South Kensington 

 Observatory, both the time of fall, I2h. 15m., and the 

 estimated region of its path being identical with the 

 above observations. 



As near as can be estimated, on consulting the region 

 on the star map, the meteor appeared some distance 

 south of the interval between Perseus and Aries, in the 

 area enclosed by a, y, |- Ceti, and fell downwards. It 

 would probably be one of the Andromedes, which were 

 due to occur on the 23rd ult. 



It was described as being as bright as Jupiter, and 

 leaving a long trail. This is fully borne out on carefully 

 examining the negative, or the accompanying enlarge- 

 ment, which is about six times the size of the original. 

 Much additional light is thrown on the phenomena 

 attending the passage of a meteorite through our atmo- 

 sphere, as at present all that is known rests on the results 

 of visual observations, which may be greatly deceptriA'e in 

 the case of such rapidly-moving objects. 



The image, in comparison with those of stars of known 



