92 report — 1859. 



' Philosophical Magazine,' June 1859, entitled " On the Periods and Colours 

 of Luminous Meteors." 



With reference to the explanations of the periodical star-showers, so often 

 attempted, the author examines the speculations of M. Charles, and, from 

 comparison with other ancient records besides those cited by that writer, 

 comes to the conclusion that his ingenious hypothesis — viz. that there may 

 be a secular progression of these periods, and that the showers of February, 

 March, and April, in the middle ages may be the same as those which now 

 recur in August — is untenable. " It rather appears that the periods remain 

 stationary, sometimes for centuries, but the transit of these streams of 

 meteors through our atmosphere is liable to interruptions and changes which 

 we may speculate upon, but cannot yet determine." — p. 2. 



With respect to the varied colours of meteors, on examining the numerous 

 results collected by M. Poey, the author suggests whether we always correctly 

 translate the names of colours used in records of such remote antiquity as 

 those of the Chinese and others referred to. He also controverts the theory 

 of M. Doppler (referred to in the last Report), and in general is disposed to 

 hold that nearly all meteors may be arranged under two grand classes, — blue, 

 and orange inclining more or less to red, while in passing from the zenith to 

 the horizon changes of colour are constantly noticed. The trains are some- 

 times of different colour from the body, and the radiation of colour over 

 objects is also often different from the colour of the meteor. 



The author very justly remarks that observers often call the same colour 

 by different names. But apart from this source of fallacy he conceives a 

 real difference possible, and " that a meteor may emit rays which in the 

 aggregate would produce one colour, and yet may affect the observer with a 

 sensation of a different colour. This may arise from absorption, intensity, 

 or contrast." — p. 7. 



He then supports this view by several arguments and instances ; in parti- 

 cular he conceives the absorption of the atmosphere, especially when satu- 

 rated with vapour, may account for the change of colour in the passage of 

 meteors, which generally terminate in red, known to be the ray most trans- 

 missible through mist. 



It has been observed by Helmholtz and others, that light of any colour, if 

 of high intensity, tends to give a sensation of tvhiteness. This the author 

 thinks will account for the radiance different from the colour of the meteor; 

 as well as for an apparent change of colour, with a change of intensity from 

 passing through a dense atmosphere. All appearances of colour are greatly 

 affected by contrast; hence he thinks the difference between the colour of the 

 bodies and trains or other products of meteors may be explained in many 

 instances. 



The author examines the question whether there may be any relation be- 

 tween period and colour in meteors. Those occurring at one period may be 

 of a different composition, and consequent colour in combustion, from those 

 at another. Such a relation is supported by many of the comparisons of 

 records made by M. Poey. The author also gives a tabular view, from 

 which it results that " August is marked by a great deficiency of orange, and 

 a great excess of blue meteors — while November exhibits comparatively few 

 blue, and a very large proportion of orange meteors, with a slight increase of 

 the red."— p. 9. 



He finally observes that all meteors, whose composition is known, consist 

 of many ingredients which may possibly all be ignited together, or separately, 

 in different instances, thus giving out different rays for each component, and 

 these again different for different intensities of combustion. In support of 

 this view he refers to the known components, iron, sulphur, and phosphorus, 



