TRANSLATORS PREFACE. Vll 



I am under very great obligations to my colleague, Dr. C. B. 

 Davenport, for kind assistance and valuable criticism, but for which 

 many defects of the translation would have been overlooked. 1 am 

 also indebted to Drs. T. G. Lee, H. B. Ward, and W. McM. Wood- 

 worth for aid in reading portions of the proof. 



E. L. MARK. 



CAMBRIDGE, MASS. 



