September 



1910J 



NATURE 



quick current often trespasses upon a slower movng one, 

 a fact which is manifested by wispy shadings and spots 

 protruding considerably into an adjacent current. Such an 

 intrusion of matter might have occurred in the region of 

 the S.S. temperate belt, and by continuing its northerly 

 course slowly but interruptedly, its rapid westerly drift 

 combined would cause it to drift in a W.N.W. direction. 

 The result would be for the matter to form a slanting 

 streak across the disc, and it is possible, and not improb- 

 able, that the oblique belt under discussion has found its 

 origin through a similar cause. 



Tests for Colour-vision. 



An article in Nature for .August 18 deals aptly with the 

 question of testing for colour-vision. It is to be hoped 

 that the committee at present inquiring into the matter 

 will advocate that testing should be carried out in future in 

 conditions resembling as nearly as possible those on which 

 seamen ordinarily follow their calling. It does not seem 

 quite practical or fair to test indoors a man's ability to 

 pick up lights in the open. The conditions of light inside 

 and outside vary so much, as do those of inside and out- 



An Oblique Belt in Jupiter, 



The movements of the seven spots lettered in the drawings 

 are tabulated as under : — 



The oblique belt was situated on the opposite side of the 

 planet to the red spot, and the longitudes of the condensa- 

 tion D might be given here : — 



April I = i69'2 I Apiil 23= 1469 



,, 6= 161 -6 May 2 = 1402 



„ 8=156-1 'I „ . 7 = 133-4 



Leeds, September 3. Scriven Bolton. 



1 Relatively to the adopted 7eri merid-an of System II., based on a rota- 

 tion pe iod of 9*1. 55111. 40 'os. (Xauticdl AlinanK). 



NO. 2134, VOL. 84] 



side darkness. A sailor's business is not to match colours, 

 but to pick up and distinguish instantly lights that may 

 be seen, far or near, through varying conditions of atmo- 

 sphere. 



The sight of the average seaman, from practice, is prob- 

 ably much keener than that of the average landsman. 

 The sailor's eyes are trained to adapt themselves to vary- 

 ing conditions of outside darkness. 



The suggestion of spectrum tests is good, provided that 

 such testing is made supplementary only to the practical 

 open-air tests with flags by day and sidelights by night. 

 The object of the tests is to ascertain the candidate's 

 faculty for instant recognition of a flag or light, and 

 there is no difficulty whatever in providing efficient prac- 

 tical tests. It is unnecessary, and even mischievous, to 

 try to puzzle a candidate with combinations of lights and 

 shades such as never occur in the course of his practical 

 work. 



It is to be hoped that the committee which is investi- 

 gating the matter will allow common sense and practical 

 ability to rule its recommendations for future examina- 

 tions. D. WlLSON-B.HRKER. 



The Thames Nautical Training College, H.M.S. 

 Worcester, Greenhithe, September 19. 



/ 



Fireball of Septeinber 2. 



The remark in N.\tl're of September 8 (p. 318), as to 

 the necessity of further observations for determining the 

 height and velocity of meteors encourages me to send 

 the following note : — 



-At g.^ p.m. on September 2, from Earlstone Common, 

 four miles south of Newbury, I had a good view of the 

 meteor described by the Rev. J. C \V. Herschel as seen 



