204 



NATURE 



[August i8, 1910 



have to trust an imperfect memory or else search 

 laboriously through original memoirs. 



Leeds, August 2. Norman R. Campbell. 



Perseid Meteoric Shower, 1910. 



The only niglit really good for witnessing the Perseid 

 shower near its maxinium this year was .August 10, when 

 the clear state of the sky afforded every facility for 

 securing observations. 



I began watching at gh. p.m., and up to iih. 4Sni. p.m. 

 there were fifty-two meteors, so that the horary rate was 

 nearly twenty, of which about three-fourths were Perseids. 

 The finest specimen appeared at loh. 6m. ; it had a long 

 and slowish (light from 328° + 37° to 301° 4-8°, and left 

 a bright streak just above the small stars of Delphinus 

 for fifteen seconds. The meteor itself was much more 

 luminous than Venus, and was also observed by Mr. T. K. 

 Jenkins at Nantyglo. From a comparison of the recorded 

 paths, I find the height 75 to 48 miles over Wiltshire, 

 and the end point near Blandford, Dorset. 



The velocity was decidedly slower than that of the 

 ordinary Perseid, its observed speed being 27 miles per 

 second. 



I saw brilliant Perseids also at 11.34 3"<1 11.46, the 

 former shortening towards a Andromedae and the latter 

 just under Polaris, and at 11.345 there was a beautiful 

 slow-moving Draconid falling from 3033° 4- 33° to 3ii°4- 

 195°. Its pear-shaped nucleus threw off a tail of yellow 

 sparks as it sailed down the sky. 



I think the display of August 10 was better than it was 

 last year, and gave promise of a pretty abundant shower 

 on .August II and 12, but I cannot speak as to its actual 

 character, the firmament being cloudy on those dates at 

 Bristol. 



There were a few breaks in the clouds on August 12, 

 and I happened to notice a fine meteor at iih. 49m. shoot- 

 ing upwards from 355° -I- 40° to 3385° 4- 50°. It was as 

 bright as Jupiter at least, and left a train, but it quickly 

 disappeared. The meteor was not a Perseid, but appar- 

 ently belonged to a shower with radiant lying eastwards of 

 a .Andromedae, or at 9° 4- 27°. The meteor was also seen 

 by Mr. G. Powell at Aberdare, and I find its height 89 to 

 53 miles. It was nearly over Bath at end point. Velocity 

 40 miles per second, and certainly more rapid than the 

 Perseid alluded to above, though it should have been the 

 swifter of the pair. 



Several observers have written me describing the Perseid 

 shower as fairly rich on August 10, though the maximum 

 was not due until the morning of, or night following, 

 August 12. Some large meteors were also recorded on 

 .August 5, which was a very clear night, and the Perseid 

 display w.is in pretty strong evidence even at that early 

 date. 



W. F. Denning. 



Brilliant Meteor of July 31. 



-An exceedingly beautiful meteor, one of the finest I 

 have seen, was observed from this vessel, while at sea, on 

 the night of July 31. The time of observation was 

 loh. om. ship's apparent time, or I3h. om. G.M.T., the 

 position of the ship at the time of observation being lati- 

 tude 43-34° N., longitude 43-37 W. The duration of the 

 flight was between fifteen and tw-enty seconds, and the 

 meteor was much more brilliant than Venus. It pursued 

 an almost horizontal course, about 8° above the horizon, 

 passing below the constellations Ursa Major, Perseus, and 

 Aries, in all traversing an arc of about 135°. 



At first the meteor appeared as a brilliant steel-blue 

 ball, with a short tail of the same colour. It disappeared 

 at a point about 90° from its first position, reappearing 

 almost immediately, and exploding and dividing into three 

 or four parts, with a luminous tail some 3° in length, and 

 of a vivid red and blue colour. Its motion was slow, 

 and it conveyed to all who witnessed it, officers and 

 passengers alike, the impression of being at no great 

 distfince from the ship when it exploded. 



Thf> night was very fine ; and the chief officer, who was 



NO. 2129, VOL. 84] 



on the bridge at the time, reports that when it dis- 

 appeared it left a small black cloud in the sky. At the 

 time of seeing this meteor we were in wireless com- 

 munication with the U.S.N. Texas, and it is hoped that 

 other observations may be forthcoming from other vessels 

 at sea. A. L. Cortie. 



On Board S.S. Cymric, August 3. 



ON COLOUR VISION AT THE ENDS OF THE 

 SPECTRUM. 



IT is half a century since Maxwell ' investigated the 

 chromatic relations of the spectral colours and ex- 

 hibited the results on Newton's diagram. The curve 

 "forms two sides of a triangle with doubtful frag- 

 ments of the third side. Now, if three colours in 

 Newton's diagram lie in a straight line, the middle 

 one is a compound of the two others. Hence all the 

 colours of the spectrum may be compounded of those 

 which lie at the angles of this triangle. These corre- 

 spond to the following — scarlet, wave-length (in 

 Fraunhofer's measure), 2328; green, wave-length, 

 1914; blue, wave-length, 1717. All the other colours 

 of the spectrum may be produced by combinations of 

 these ; and since all natural colours are compounded 

 of the colours of the spectrum, they may be com- 

 pounded of these three primary colours. I [Max- 

 well] have strong reason to believe that these are 

 the three primary colours corresponding to three 

 modes of sensation in the organ of vision, on which 

 the whole system of colour, as seen by the normal 

 eye, depends." 



Later observations, such as those of Konig and 

 Dieterici,- have in the main confirmed Maxwell's con- 

 clusions. The green corner is indeed more rounded 

 off than he supposed. It is with regard to the 

 " doubtful fragments of the third side " that I have 

 something to say. According to Maxwell's results 

 with both of his observers the extreme red deviates 

 from the less extreme by a tendency towards blue. 

 Neither my friends ^ nor I can perceive anything of 

 this. When the extreme and the less extreme red 

 are seen in juxtaposition in the colour-box, no differ- 

 ence whatever can be perceived after the brightnesses 

 are adjusted to equality. I have not any precise 

 measurements of wave-length, but the extreme red 

 passed a cobalt glass while the less extreme was 

 stopped. Observations at the ends of the spectrum 

 are more difficult than elsewhere. Owing to deficiency 

 of illumination at these parts there is more danger of 

 false light finding access. To get satisfactory results 

 I found it desirable to supplement the action of the 

 prisms by placing red glass over the slits. It is prob- 

 able that Maxwell was misled by some defect of this 

 sort, since the differences he found would appear to 

 lie outside the errors of observation. The German 

 observers, it should be added, also found the colour 

 constant at the red end. 



At the other extreme the tendency of the violet 

 towards red is, to mv vision, not in the least doubt- 

 ful. Some remarks made a few years ago by Dr. 

 Burch, who speaks of violet in terms which I could 

 not possibly use, were the occasion of a more par- 

 ticular examination. Although, so far as I remem- 

 bered, I had never made the trial, I was confident 

 that I should be able to match violet approximately 

 with blue plus red, and full blue with violet phtx 

 green. And it seemed further that this must be the 

 general estimation, as there is no widely spread protest 

 against describing the upper extreme of the spectrum 

 as "violet" — a name which would be quite inappro- 

 priate in the absence of an approach towards red. 



1 Phi'. Trans.. iSfo. 



2 Helmholt7, " Phys. Optik," 2nd edition, p 340. 

 •' Mr. Gerald Balfour included. 



