Proceedings. 89 



PHYSICAL AND MATHEMATICAL SECTION. 



Ordinary Meeting, January i8th, 1888. 



Dr. BOTTOMLEY in the Chair. 



Dr. BOTTOMLEY stated that he wished to call attention 

 to an error in his paper, " On the Composition of projections 

 in geometry of two dimensions," published in Vol. X., 3rd 

 series of the Society's Memoirs; on page 15, it is stated 

 that the perimeter of the ellipse 



nf\x - of + /\vil{x - d)y + (4 - yn^))/"" = wV^ 

 is equal to the perimeter of the circle 



{x-af-v^y-hf^c"^ 

 from which it is derived — this, however, is not correct, the 

 axes of the ellipse are ^(i +/) and ^(i — /), and the statement 

 holds only in the case when /= 0, it will, however, be approxi- 

 mately true if / be a very small quantity, using a method of 

 approximation adopted in some mathematical tables. 



