250 Mr. J. N. Lockyer. On the Classification [Jan. 10, 



and passing a magnet through the insoluble residue. In the oxy-coal- 

 gas flame the spectrum of the spherules consisted of lines of iron, 

 sodium, and potassium, and the flutings of manganese, but there was 

 absolutely no trace of thallium. The other portion of the residue, 

 however, gave the thallium line as bright as the nodules themselves. 

 The solution, when evaporated to dryness, gave no indications of 

 thallium. 



If we are justified in regarding the partly meteoric origin of the 

 nodules as established, the excess of thallium shows that each nodule 

 represents a very considerable quantity of meteoric dust, since there 

 is only a comparatively small proportion of thallium in meteorites. 

 This further suggests that an enormous quantity of meteoric dust 

 passes through our atmosphere, especially as that which falls on the 

 sea only represents a portion of the total amount. 



III. " SUGGESTIONS ON THE ORIGIN OF BINARY AND 

 MULTIPLE SYSTEMS." 



In connexion with the explanation of the variability of the bodies 

 of Group II, which I suggested in the Bakerian Lecture for the last 

 year, I indicated that in the absence of spectroscopic details, the 

 colours of the components of double stars might enable us to deter- 

 mine whether both have condensed from double or multiple nebulas, 

 or whether the companions are later additions to the systems. I also 

 referred to some difficulties in the discussion. 



On further consideration some of the difficulties have disappeared, 

 and I now propose to return to the subject, limiting myself for 

 greater simplicity to binary systems. 



For this purpose it is necessary to begin by stating briefly what we 

 know relating to the colours of the different groups of celestial bodies, 

 adopting the classification which I suggested in the Bakerian 

 Lecture. 



I. Colour Phenomena. 



As far as we at present know, the colours associated with the 

 different groups of celestial bodies are in all jirobability as follows : 



Group I Blue, greenish blue, white, or pale grey. 



Group II Yellowish red. 



Group III Yellow to greenish white. 



Group IV Bluish white. 



Group V Greenish white to yellow. 



Group VI Reddish yellow to blood red. 



Group VII Dark or nearly dark bodies. 



