I wish to avail myself of this opportunity to acknowledge 

 my obligation to each member of the Mathematical Faculty 

 of Clark University and to Dr. A. G. Webster of the 

 Department of Physics of the same institution for their 

 continued assistance and inspiration during the three years 

 in which I have attended their lectures; and I desire 

 especially to express my gratitude to Professor W. E. Story 

 for the suggestions which led to the subject of this paper 

 and also for the constant help and stimulation so kindly 

 and generously given in the working out of the results 

 here presented. 



Christiania, March 28th, 1899. 



Frederick C. Ferry. 



