288 



Prof. H. A. Nicholson on the Errant 



[May 8, 



the atmosphere of some stars ; and it is suggested that the phenomena of 

 variable stars may be due to a delicate state of equilibrium in the 

 temperature of a star, which now produces the great absorption of the 

 compound and now that of the elemental molecules. 



II. Mechanical Mixtures. 



The second part of the paper deals with the mechanical mixtures. 

 Maps of the spectra of alloys of the following percentages are given : — 



Sn and Cd percentages of Cd 10-0, 5-0, 1-0, 0-15. 

 Pb and Zn „ „ Zn 1O0, 5-0, 1-0, 0-1. 

 Pb andMg „ „ Mg 10*0, 1-0, 0-1, 0-01. 



It is pointed out that the lines disappear from the spectrum as the 

 percentage becomes less, the shortest lines disappearing first — and that 

 although we have here the foreshadowing of a quantitative spectrum- 

 analysis, the method is so rough as to be inapplicable. 



It is then stated that further researches on a method which promises 

 much greater accuracy are in progress. 



The bearing of these results on our knowledge of the reversing layer 

 of the sun's atmosphere is then discussed. 



III. " Contributions to the Study of the Errant Annelides of the 

 Older Palaeozoic Rocks." By H. Alleyne Nicholson, 

 M.D., D.Sc, M.A., Ph.D., F.R.S.E., Professor of Natural 

 History in University College, Toronto. Communicated by 

 Professor Ramsay, E.R.S., Director- General of the Geological 

 Survey of the United Kingdom. Received December 30, 

 1872. 



(Abstract.) 



In this communication the author endeavours to elucidate the 

 abundant and obscure organic remains which are found so commonly in 

 the Palaeozoic rocks, and especially in the Silurian strata of Britain, and 

 which are generally known by the vague and convenient names of 

 "Fucoids," " Annelide-burrows," and "tracks." After expressing his 

 opinion that the first step towards the study of these obscure fossils lies 

 in the provisional grouping and naming of the more marked forms which 

 are already known to exist, the author proceeds to divide the remains 

 under consideration into two great groups. In the first of these groups 

 are those fossils which are truly the burrows of marine worms, as distin- 

 guished from mere trails and surface-tracks. Some of these burrows 

 (Scolithus) are more or less nearly vertical in direction as regards the 

 strata in which they are found ; and they are to be looked upon as being 

 true burrows of habitation. In this section are placed the genera 

 Scolithus, Arenicolites, and Histioderma. Other burrows are of a totally 



