296 Mr Herschers Table of the 



must assume a nebulous appearance when situated at immense 

 distances ; but whether all nebulous appearances are occasion- 

 ed by stars, is a problem apparently beyond the reach of man 

 to resolve, without the assistance of analogy, which ought not 

 to be trusted too freely, especially with objects almost equally 

 beyond the reach of our hands and telescopes. Several of the 

 very faint and delicate nebulae can be resolved into stars, and 

 also many of the brighter nebulae are composed of stars ; but 

 there are a greater number which have not yet been resolved 

 or shown to consist of stars ; and it is not improbable, that 

 " shining matter may exist in a state different from that of the 

 starry." 



Art. XV. — Table of the Refractive Powers of several Bodies, 

 according to the observations of J. F. W, Herschel, Esq, 

 F. P. R. S. Sfc. With remarks by the Editor. 



In his Treatise on Light, Mr Herschel has published a very 

 copious table of refractive powers, compiled from the observa- 

 tions of preceding authors, and he has inserted in it vari- 

 ous observations of his own, which, from the accuracy with 

 which they were made, possess very great value. From the 

 importance which is now beginning to be attached to the opti- 

 cal properties of minerals, as affording the most precise dis- 

 tinctive characters, both our optical and mincralogical readers 

 will be glad to see these measures of Mr Herschel collected 

 from the table in which they occur. 



Table of Mr HerscheVs Measures of the Refractive Powers of 

 several Bodies*, 



Saturated aqueous solution of alum, - - 1 .356 



Alcohol (rectified spirits,) _ _ - J. 372 



Muriatic acid (spec. grav. 1.134,) - - - 1.392 



Sulphuric acid, - - - - 1.430 



Oil of turpentine (common,) - . - 1.486 



Oil of olives, - - - - * ' 1.4705 



Nut oil (perhaps impure,) , . _ 1.490 



* From his Essay on Light, §.1116. 



