140 



base. Moreover, long experience has proved that for the 

 production of electric light the alternating current is greatly 

 superior to the continuous one, as commutators are dis- 

 pensed with, and it has the important advantage of con- 

 suming the carbons equally, and thereby always retains the 

 luminous point in the focus of any optical apparatus used 

 in connection with it. 



In short, M. Gramme, in his endeavour to reconcile the 

 incompatible relations of the voltaic current and the 

 magneto-electric wave at the instant of its generation, has, 

 by inverting the order and functions of the organic parts 

 of an ordinary magneto-electric machine and suppressing 

 the action of a number of the armature helices, brought 

 about results retrogressive from those previously attained 

 by NoUet, Berlioz, and Holmes, and it is only by the 

 adoption of the principle of electro-dynamic accumulation 

 (i.e., the exciting of a major electro-magnetic induction 

 machine by a minor one, fixed on the same base), in accord- 

 ance with the principles laid down by the author in his 

 former papers, that the results obtained by M. Gramme 

 exceed those from ordinary magneto-electric machines. 



PHYSICAL AND MATHEMATICAL SECTION. 



April 22nd, 1873. 



AlfPvED Brothers, F.RA.S., President of the Section, in 



the Chair. 



Results of Rain Gauge Observations made at Eccles, near 

 Manchester, during the year 1872, by Thomas Mackereth, 

 F.R.A.S., F.M.S. 



The characteristic of the rainfall of the past year is its 



