TRAN8LATOB8 PREFACE. VU 



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. I am 

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

 worth for aid in reading portions of the proof. ' 



. ■&. L. HABK. 



Cambbjsge, Mass. 



