We present ultra-high-resolution (R = 900000) observations of interstellar
Na I and K I absorption lines towards kappa Vel (HD 81188) which show clear
evidence for temporal variation between 1994 and 2000, Specifically, the c
olumn densities of K-0 and Na-0 in the main velocity component have increas
ed by 40 and 16 per cent, respectively, over this period. Earlier work had
suggested that this component actually consists of two unresolved sub-compo
nents; this result is confirmed here, and the overall line profile is found
to be consistent with only one of these sub-components having increased in
strength since 1994. We argue that this variation is consistent with the l
ine of sight gradually probing a cold, dense interstellar filament of the k
ind recently proposed by Heiles to explain other observations of small-scal
e structure in the interstellar medium.