532 The Astronomer Royal's Remarks 



do not surprise us, for they result simply from the fact of the 

 equality of the atomic volumes with respect to the isomorphous 

 compounds, we meet with a number of most striking anomalies. 

 For the chlorides of calcium, strontium and magnesium, the 

 atomic volume is equal to 1 1 multiplied by 6, i. e. the number of 

 equivalents of water of crystallization of those salts, but for the 

 alums it is 11 x 25, while there are only 24 equiv. water. For 

 the sulphate and borate of soda with 10 equiv. water the vo- 

 lume = 11 X 10, but for the pyrophosphate with 10 equiv. 

 water it is 11x11; and for the carbonate likewise, with 10 

 equiv. water, it is 9*8x10; for the anhydrous carbonate of 

 soda the factor 11 is taken, and for the hydrated carbonate 

 9*8 ; on the contrary, for the anhydrous sulphate of soda the 

 authors prefer 9*8, and for the hydrated sulphate 1 1 . The bro- 

 mide of potassium =4x 11, the bromide of sodium =5x11, 

 the chloride of potassium =4x9*8, the chloride of sodium 

 = 3x9*8. 



These instances we think will suffice to show that the hy- 

 pothesis of Messrs. Playfair and Joule is not confirmed by an 

 analogy of formulas such as ought to be expected, and that 

 the coincidence which does exist between the calculated and 

 the observed densities merely result from the easy way in which 

 the authors select at will the factor 9*8 or the factor 11, or 

 even of combining them for one and the same body, as they 

 have done in a large number of cases. 



LXXXI. Remarks on Dr. Faraday's Paper on Ray-vibrations. 

 By G. B. Airy, Esq., Astronomer Royal. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



THE communication which accompanies this was sketched 

 before my attention was called to Dr. Faraday's leading 

 paper in your Number for the present month. I need not to 

 say that I read that paper with great interest and great plea- 

 sure. Yet I will ask your indulgence, and I am sure that I 

 shall receive the forgiveness of Dr. Faraday, while I comment 

 on the principal points of that paper somewhat critically. I 

 am desirous of examining, or of suggesting grounds for exa- 

 mination by others, as to how far the fundamental supposi- 

 tions of Dr. Faraday are necessarily limited by recognised 

 phagnomena, and as to how far the subject is metaphysical or 

 physical. 



The paper, as I understand, treats of two subjects : — 



1. The possibility of explaining phenomena of radiation, 



