230 Wisconsin Academy of Sciences , Arts and Letters. 
the time covered by his observations. Kuestner adopted the latter al¬ 
ternative, but his suggestions were received with great incredulity on the 
part of astronomers, and it was only when it became apparent that sim¬ 
ilar changes could be traced in simultaneous observations elsewhere that 
the matter seemed worthy of serious investigation. Such investigation 
it has received under the auspices of the International Geodetic Associ¬ 
ation, which has for over two years past maintained a continuous series 
of observations at three German observatories, which agree in indicating 
a variation of the latitude of these stations in character entirely similar 
to that detected by Kuestner. In our own country similar investigations 
have been prosecuted in a less systematic manner, but agreeing never¬ 
theless with the results of the German work. 
But we come here to a new phase of the matter. An extended and 
very elaborate discussion of long series of astronomical observations 
running back over a period of more than a century has been undertaken 
by Mr. S. C. Chandler, who has reached the very remarkable result that 
during this entire period traces of a similar variation in latitudes may be 
detected, that is, that during this period the latitude of any given place 
on the earth’s surface, instead of being absolutely fixed, has oscillated 
about a mean value, being at times a little greater and at others a little 
less than its average amount. 
If we inquire into the causes of such an instability of latitude, we shall 
find very serious difficulties in the way of any explanation based upon 
known dynamical laws. It is true that Euler pointed out a century ago 
that if the axis about which the earth rotates does not coincide exactly 
with its axis of figure, that is the short diameter of the spheroidal earth, 
there will necessarily result a rotation of one of these axes about the 
other producing a slight periodic change in latitudes, and that this 
change should run through its complete cycle in a period of 308 days 
But it seems difficult at first sight to identify this theoretical oscillation 
with the actual changes detected by the European observers and by Mr. 
Chandler. The work of the European observers appeared to indicate an 
oscillation of latitudes having a period of very approximately a year, 
while the time required for the periodic change detected by Chandler is 
427 days; so that the periods appear to be entirely discordant. A sugges¬ 
tion has been made in this connection, however, by Professor Newcomb 
which may help to bridge over the difficulty of co-ordinating these periods 
among themselves. He points out that the period of 306 days which is 
associated with Euler’s name has been computed upon the supposition 
that the earth is a perfectly rigid body, while we have abundant evidence 
that the earth’s rigidity, although great, is by no means infinite, and this 
lack of perfect rigidity will have the effect of lengthening the Euler 
period, so that it may be made 365 days or 427 days long, thus possibly 
bringing it into agreement with the observed periods. One difficulty 
