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 \sim 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 .