TABER. — ON SINGULAR TRANSFORMATIONS. 697 



Parameter group discontinuous ; also group 



9 9 9 9 9 9 9 



0" Xi cy aro d x^ d Xi d Xo 9 x^ 9 x^ 



xype i. I ^^^.^^ ^^^^ _ ^^ ^^^^ ^-^.^^ _ ^^ ^^^^ ^^^ _ ^^ 



All groups of this type are continuous. 



P. S. Since what precedes was written, I have found that the infiu- 

 itesinaal transformations of the parameter group, given in equations (13), 

 § 2 (from which follow the differential equations (16), §3), had already 

 been obtained by Schur and Engel ; and that to Engel is due the deter- 

 mination of the values of the a's for which A„ = 0. See Lie : Trans- 

 formationsgruppen, III, pp. 760, 794. 



June 8, 1900. 



