TRANSLATOR'S rui vii 



I am iimlcr v-ry 'gn at obligations to my colleague, Dr. C. B. 

 nport, for kind a.-sistam-e- ami valuable criticism, "tit for which 

 many defeota of the tranalatipn would have l"rn overlooked. 1 am 

 idflo indebted to Drs. T. G. Lee, H. B. Ward, ami \V. McM. Wood- 

 worth for aid in reading portions of the proof. 



E. L. MARK. 



CAMBKIDGK, 



