July 2 1, 1881] 



NA TURE 



:6i 



I examined carefully, some weel s a,L;o, some extensive heaps 

 of sand and gravel rai-ed on the premises of the Water-\\orl;s 

 Company on the right aci-ofs the Hammersmith Su'ipennon- 

 hridge, but f aind no worked flints. The "ravel here may he of 

 more recent deposition. 



With regard to the Neolithic implemer.ts 1 f Acton, I am 

 interested to hear that Mr. Worthingtoi Smith is familiar with 

 them, and that there are specimens in ihe Pitt-Rivers Collection. 

 My letter nevertheless will have done good in making their 

 occurrence more generally known. 



As regards the quartzite pebble, if more are found on the fields 

 about Acton it h ill tend to show that they have served the same 

 purpose as those in Scuth-East Devon, and that they have been 

 brought from a region where specimens adapted for missiles 

 would be found in aljundance, viz. the south-west coast, as gravel 

 sections and gravel pits were not accessible in Neolithic times, 

 nor would they have proved adequate arsenals. But if the pehble 

 I found at Acton were accidentally derived from the Middlesex 

 gravel (which contains a considerate quantity of Midland Bunter 

 material),^ it is remarkable that a selection should have been 

 made so well calculated to deceive a Devonshire iieolithcjlogist. 



July 19 Spencer Geo. Perceval 



Lightning 



About 10 a.m. of the 6ih insiant two of ihe labourers on this 

 farm were sitting on the ground (wi'h iheir backs against a 

 clover haystack and iheir faces towards the north, having in 

 front of them and on their left a \> ood) engaged in eating their 

 lunch. It had been rainin;; and thundering for about half an 

 hour, but not heavily, until suddenly — in the words of one of 

 the men — "a flash of lightning came ri-ht at us as if it w'ere 

 shot out of a gun." This man had his knife up to his mouih at 

 the time in the act of eatiui;, .and he dccribes his sensation as a 

 feeling of nausea in his throat aiid chest, and also that both he 

 and his companion felt an actual push against their shoulder'^, 

 which sv\ayed and shook ihem to a considerable extent from the 

 direction of the flash. The other man was blinded for about 

 five minutes, and they were both njuch dazed for some time. 

 Also they both de cribe having heard a harp whiz somewhat 

 resembling the quick csca]ie of steam from an escape valve en 

 an engine. For two days after they both suffered from severe 

 headache. A. Hall, jun. 



Filstone Hall, Shoreham, Kent, July II 



THE COMET 



TN a paper read to the Paris Academy on the nth 

 ■*■ inst., giving further observations on comet b iSSi, 

 M. Wolf says :— 



"The analysis of the light of the comet furnishes data 

 as to the constitution of that body, which it is important 

 to consider before starting any hypothesis as to its 

 nature and mode of evolution. 



" I have examined the spectrum of the comet, both 

 with a highly dispersive spectroscope mounted on the 

 Foucault telescope of o'4o m. aperture, and with a smaller 

 instrument, mounted on the telescope of r2om., giving 

 therefore a very large quantity of light. This spectrum 

 is triple: one sees (1) a continuous spectrum, broad, but 

 very pale, visible in all the regions of the comet ; (2) a 

 continuous spectrum nearly linear, and very bright, given 

 by the nucleus ; (3) the spectrum of thiee bands, yellow, 

 green, and blue, chara -teristic of the light of all comels 

 examined hitherto. I have never been able to see the 

 violet band. 



"The continuous sfectrutn of the nucleus indicates the 

 existence of solid or liquid matter, luminous of itself or 

 by reflection. 1 have suspeced in the strip some dark 

 interruptions, especially in the region near D, without 

 being able to determine their position. The presence 

 of these dark lines, demonstrated by Dr. Huggins' photo- 

 graphs, denotes a reflected light, which can be no other 

 than that of the sun. 



"The nebulosity which forms the head of the comet 

 gives, besides the continuous pale spectrum, the bright 



bands of an incandescent compound gas. Tiie researches 

 of M. Hasselberg tend to assimilate these bands to those 

 of a carburet of hydrogen, probabl)- acet\lene. Besides 

 these bands one sees throughout the strip formed by the 

 light of the nucleus other protuberances very short, and 

 paler, which seem to indicate, in the hotter and more 

 luminous parts of the comet, an incandescent atmosphere 

 of more complex constitution. 



"When the slit of the spectroscope is passed over the 

 comet, starting from the head, one finds the three bands 

 all round the nucleus, at nearly the same distance from 

 all the sides. They disappear in the tail properly so- 

 called, the very pale spectrum of which seems to be 

 continuous. Thus only the nebulosity surrounding the 

 nucleus contains incandescent gases. The light of the 

 tail comes to us from a pulverulent matter, luminous, or 

 simply illuminated. Such are the data of spectroscopy. 



"The polariscopic examination of the comet's light com- 

 pletes these first results. I used, as polariscope, a quartz 

 plate perpendicular to the axis, giving the sensible tint, 

 and a double-refracting prism, placed between a collima- 

 tor and an observing telescope, in place of the prism of 

 a direct-vision spectroscope. The two images of the 

 nucleus and the nebulosity surrounding it are projected, 

 well separate, on the common part of the field formed by 

 the background of the sky : this is the process indicated 

 long ago by M. Prazmowski for eliminating atmospheric 

 polarisation. Under these conditions the nucleus and 

 the nebulosity appear both distinctly polarised in the 

 median plane of the tail, consequently in the plane pass- 

 ing through the sun. Here then, at least in all parts of 

 the nebulosity round the nucleus, we have reflected light 

 coming froin the sun, and a nongaseous matter possessed 

 of reflecting power. I have had this important result 

 verified by my assistant, M. Gudnaire, and by several 

 students in the Observatory. 



"This process, so sensitive, evidently cannot serve for 

 the tail, which occupies the whole field of vision, and does 

 not moreover present very distinct limits. I have vainly 

 tried other polariscopes — Savan's, for example. It would 

 be very difficult besides to separate here the real polarisa- 

 tion of the tail from th it of the atmosphere. 



" In proportion as the light of the comet is diminished, 

 the spectrum of the nucleus bccoincs paler ; its colours, 

 well pronounced on the earlier days, are no longer seen 

 except on the side of the red ; the bright bands retain 

 their brightr.ess. The green band is always distinctly 

 limited in the less refrangible part. It will be interesting 

 to know whether the comet, reduced to telescopic bright- 

 ness, will at the same time have its light reduced to that 

 of an atmosphere purely gaseous. 



" On June 29, at 5h. 49m. sidereal time, during my 

 polariscopic observations, a small star was found in the 

 nebulosity, at a very short distance from the nucleus. Its 

 image had not undergone any change, either of brightness 

 or of form." 



At the same seance M. Thollon cominunicated a note of 

 spectroscopic observations of the comet as follows : — 



"These observations were made with a direct-vision 

 spectroscope which MM. Henry of the Observatory were 

 good enough to lend me. The dispersion is that of an 

 ordinary prism. A micrometer eye-piece, with point, giving 

 i-200th of a millimetre, enables one to make measure- 

 ments of very high precision. 



" In the night of June 24 I made my first observations 

 and measurements. The nucleus presented then a very 

 brilliant continuous spectrum, on which no trace of bands 

 could be distinguished. On the violet side it extended 

 beyond the line G. The parts next the nucleus liken ise 

 gave a continuous spectrum, on which the bands were 

 still invisible ; they only appeared a little further on and 

 faintly. In the continuous spectrum I have thought I 

 perceived several times a very complicated system of dark 

 lines, and occasionally 1 believed I saw in the spectrum 



