178 Mr. Thompson on the Soluhilitfj of 



But it is not to be inferred that the ratio of the intensities 

 of the two systems will remain the same at all distances. 

 Were the refracted light in one plane (instead of having a 

 vertical divergence of 6°), and were the reflected light com- 

 prised within a cone uniformly illuminated (which is not the 

 case), the light from the first would vary inversely as the di- 

 stance, from the second inversely as the square of the sum of 

 the distance and a constant which depends upon the diver- 

 gence; but neither of these conditions being fulfilled, the re- 

 spective illuminations must vary with the distance according 

 to two other distinct laws, each much more complicated. It 

 is clear, therefore, that the comparison made at one given di- 

 stance will not apply to any other given distance. But still 

 the effect of distance in modifying intensity, may be much 

 more accurately estimated in the case of the prismatic than of 

 the reflecting arrangement. 



The following conclusions seem to be warranted : 



1. That, at a distance of thirteen miles, the mean effect of 

 the new light is very much superior to the mean effect of the 

 old light (perhaps in the ratio of two to one). 



2. That at all distances the new light has a prodigious su- 

 periority to the old, from the equality of its effects in all azi- 

 muths. 



3. That the new light fulfils rigorously the conditions re- 

 quired for the distribution of light to the greatest advantage. 



4. That at distances much exceeding thirteen miles, the 

 new light must still be a very effective one, though to what 

 extent the Committee have not observed. The light is under- 

 stood to be still a good one, when seen from Edinburgh at a 

 distance of about thirty miles. 



XXXVIII. Remarks on Mr. Brett's Experiments on the Solu- 

 bility of Metallic Oxides and Salts in Muriate and 'Nitrate 

 of Ammonia. By L. Thompson, Fjsq^.^ Member of the lloyal 

 College of Surgeons, 



To the Editors of the Philosophical Magazine and Journah 



Gentlemen, 

 T OBSERVE a serious omission in the laborious experi- 

 -■• ments of your correspondent, Mr. Brett, on the solubility 

 of metallic oxides and salts in muriate and nitrate of am- 

 monia, inserted in your last Number, p. 95, which, if uncor- 

 rected, is likely to produce an erroneous opinion as to the 



