Intelligence and Miscellaneous Articles. 557 



hydrogen spectrum diminishes by about 0*0003 between the limits 

 of 10° and 95° C. for water and aqueous solutions. 



(5) At the same temperature the refracting-power of solutions of 

 the same salt is less the more concentrated the solutions. For each 

 salt dissolved the maximum of the refracting-power is equal to that 

 of distilled water, which is 0'7812 at 4° C. Solutions equally con- 

 centrated of different salts are far from having the same refracting- 

 power. Thus a solution of chloride of calcium the standard of 

 which is 0*326 has a refracting-power higher than that of a solution 

 of nitrate of lime one-seventeenth as strong. There is, however, a 

 singular exception to this rule : solutions of chloride of lithium have 

 a higher refracting-power than that of distilled water; and the more 

 concentrated the solution, the higher it is. These solutions are also 

 remarkable for their coefficient of expansion, which is less than that 

 of distilled water, and changes very little for considerable variations 

 in the standard of the liquid. 



Biot and Arago's law does not apply rigorously to saline solu- 

 tions ; yet in most cases it is sufficiently close, and furnishes for 

 each solution a characteristic number representing its refracting- 

 power. Of a hundred and twenty-three solutions which I investi- 

 gated, there are only sixteen where the observed error exceeds the 

 probable limit of error, and of these sixteen there are fourteen where 

 it is exceeded by only a small quantity. Only in the case of two 

 solutions of chloride of zinc is the discrepance between the calcu- 

 lated and the observed results too great to be attributed to accidental 

 errors : the great affinity of chloride of zinc for water, and the 

 formation of different hydrates in the solution, explain sufficiently this 

 apparent anomaly. Among the salts I have investigated, the solu- 

 tions of two only (chloride and carbonate of lithium) have a refract- 

 ing-power higher than the refracting-power of distilled water. — 

 Comptes Rendus, Jan. 21, 1867. 



ON THE ESTIMATION OF STAR-COLOURS. 

 BY SIDNEY B. KINCAID, ESQ. 



The author remarks that, with the exception of the two isolated 

 instances of Sirius and 95 Herculis, the latter of them due to the 

 researches of the late Admiral Smyth and the Astronomer Royal for 

 Scotland, no crucial example of the change of the colour of a star 

 has been determined, although there is every reason to believe that 

 such objects vary as well in their hues as in their apparent brillian- 

 cies. That physical astronomy, which has made such strides in 

 relation to the "variables," has done so little in the matter of side- 

 real chromatics is certainly not owing to any lack of interest on the 

 part of the latter subject of inquiry, but is owing to the difficulties 

 that beset any attempt at accurate chromatic observation. Until 

 the publication of the late Admiral's last work, which was specially 

 devoted to the " Colours of Double Stars," no general system for 

 reducing such observations to permanent record in connexion with 



