We present the results of a GHRS program to monitor the absorption lines in the spectrum of the Seyfert 1 galaxy NGC 4151 caused by outflowing gas from the nucleus .
Although we see subtle changes over the four year period in the GHRS spectra of the broader of the absorption features , the wavelength constancy of all the features is remarkable .
The limits on the secular acceleration suggest that either ( 1 ) The absorbing clouds are well beyond the broad emission line region , or ( 2 ) The clouds are experiencing significant drag from an intercloud medium .
The exception to this constancy occurred during one of the epochs of our monitoring when a broad shallow C IV trough appeared at an outflow velocity of 3750 km s ^ { -1 } and then subsequently disappeared .