THE LATITUDE-VARIATION TIDE.* 
BY 
Alexander Smyth Christie. 
[Read before the Mathematical Section May 23, 1895. The non-mathe- 
matical part was read before the Society May 11, 1895.] 
I. 
The Derivation of the Formulx. 
Let 
H = h + 2 (c r cos i r t -j- s r sin i r t) 
r 
= h-\- Z a r COS (i r t — e r ) 
r 
be the height of the surface of the sea at time t above any 
datum plane, then for a series of v observations at equal time 
intervals r we have, t denoting the middle of the series, 
* General W. W. Duffield, Superintendent of the United States Coast 
and Geodetic Survey, has very courteously granted me permission to 
publish the data given below, and has also favored me with copies of 
several papers on file in his office prepared by me while engaged in the 
search for this tide. A paper containing the full discussion is reported 
to him by his subordinates as not found. 
15-Bull Phil. Soc., Wash., Vol. 13. 
(103) 
