PEEFACE TO SECOND EDITION.
THE present edition is entirely the work of my father-in-law,
the late Dr. CASEY, F.R.S. At the time of his death., in
1891, he had seen nearly 400 pages of it through the
press, and left me the responsibility of bringing out the
remainder.
In the preparation of this edition Dr. CASEY had the
valuable assistance of Professor NEUBERG of the Univer-
sity of Liege, who sent him numerous important theorems,
notes, and suggestions, almost all of which he adopted.
Knowing that Professor NEUBERG was Dr. CASEY'S inti-
mate friend and constant correspondent, and that he had
assisted him in correcting all the proof-sheets of what
had been printed prior to his death, I naturally turned to
Mm for advice and aid before proceeding with the printing
of the remaining portion. He most willingly promised
me his valuable assistance. Having revised the proofs,
I submitted them to him, and he had the kindness to
correct them and approve of them, before they were
printed off.
For all his generous help and advice I beg to re-
turn Professor NEUBERG my grateful acknowledgments
and very sincere thanks. I have also to thank the
Eev. EGBERT CURTIS, s.j., F.R.U.I., for many useful sug-
gestions, and for the trouble he took in revising the
proofs.