  We have analyzed Rossi X-ray Timing Explorer Proportional Counter Array
observations of the pulsed emission from SGR 1900+14 during September 1996,
June - October 1998, and early 1999. Using these measurements and results
reported elsewhere, we construct a period history of this source for 2.5 years.
We find significant deviations from a steady spin-down trend during quiescence
and the burst active interval. Burst and Transient Source Experiment
observations of the burst emission are presented and correlations between the
burst activity and spin-down rate of SGR 1900+14 are discussed. We find an 80
day interval during the summer of 1998 when the average spin-down rate is
larger than the rate elsewhere by a factor ~ 2.3. This enhanced spin-down may
be the result of a discontinuous spin-down event or ``braking glitch'' at the
time of the giant flare on 27 August 1998. Furthermore, we find a large
discrepancy between the pulsar period and average spin-down rate in X-rays as
compared to radio observations for December 1998 and January 1999.
