660 Notices respecting New Books. 
relatively to the other rays from radium, of much more importance 
than was held hitherto to be the case. Again, we find throughout 
Professor Soddy’s book the a particle spoken of as having the 
dimensions of the material atom, with nothing to suggest the quite 
different view put forward by Mr. Harold Wilson during the 
present year. 
This, in common with other works dealing with the rapidly 
advancing science of Radioactivity, will require frequent re-editing. 
A solid and valuable body of experimental work, with which new 
views must ultimately be brought into harmony, is, however, care- 
fully and ably described in this volume. J.J. 
Astronomical and Historical Chronology in the batile of the Cen- 
tures. By WittiaM Luicuron Jorpan, F.B.GS., LSS., &e. 
(Longmans, Green & Co.) 
Fw questions seem so simple and yet really are so complicated as 
questions of chronology. And here we are not alluding to the 
many different eras which have been used in different parts of the 
world and in different periods of the world’s history, from which 
to express the date of any event we desire to chronicle or discuss, 
In all Christian countries for many centuries past (not, be it re- 
membered, during the four or five immediately following that 
event) the birth of Christ, or the date at which it was supposed 
to have taken place, was the initial point from which all other 
events were dated, either before or after it, necessitating the use 
of the symbols B.c. for before, and a.p. for after the Nativity. It 
is now generally recognized that when this era was first intro- 
duced a mistake was made with regard to the year in which it 
took place, and that our Lord was really born probably in B.c. 5. 
That, however, is not the point which is especially discussed in 
the volume before us. 
The assumed date of Christ’s birth is generally supposed to have 
been about the end of the year which we now reckon as B.c. 1 
(the interval between the recognized Christmas Day and the end 
of the year as settled by the Julian Calendar is too short to be 
worth taking into account), so that a.p. 1 was then commenced 
and completed on December 31 of that year. According to this 
one century was completed on Dec. 31, a.p. 100, and nineteen 
centuries on Dec. 31, a.pv. 1900. The writer of this notice well 
remembers a letter being written from some unknown corre- 
spondent to the late Sir George Airy, then Astronomer-Royal, 
asking him to resolve a dispute when the twentieth century would 
commence, and the answer was that “avery little thought” 
would show that it would commence on Jan. 1,1901. The book 
now before us takes a different view, and the Author does not 
forget to remind us that the German Emperor some time ago put 
forth a dictum that the twentieth century began on Jan. 1, 1900. 
Mr. Jordan, recalling the fact that those medieval writers who 
first used Christian chronology reckoned not from the Birth, 
