125 



The elegance of this formula of Mr. Herschel, and the important 

 consequences which he has obtained from it, have induced us to 

 shew how the same expression may be derived from the develop- 

 ment of the characteristic function of an ordinary system of revolu- 

 tion, assigned in the present Supplement. The same form of deve- 

 lopment, and those other forms which we have assigned in the same 

 Supplement, for systems not of revolution, contain the solution of 

 other optical problems, of which we hope to treat hereafter. 



Vol. XVI. 



