subroutine partvl - j.f.chandler - 1980 jan 14
apply scale factors to obtain velocities as derivatives
w.r.t. observer's coordinate time.  see memo by jfc
"the light-time correction to partial derivatives in pep"
dated aug 28, 1978.  these partial derivatives of the
velocities are not exact (as are the velocities themselves)

der  - array of partials, either send/receive or reflect
n    - indicator of type of array
n=2 -> apply dt3/dt1 to send-reflect leg
n=1 -> apply dt2/dt1 to (only) leg
kick - type of observation series
kick =1 subroutine radar is calling program
kick =2 subroutine optic is calling program
kick =3 subroutine trnsit is calling program
kick =4 subroutine fermtr is calling program