, but this is easy to do with a continuum lamp exposure through a small decker to define the spectral trace. The guide camera images indicate, and the spectra confirm, that the last three object exposures drifted by 1.5 arcseconds relative to the position shown in Fig. 15, so these were not used in the final analysis. In all, the total exposure time for the spectra is 140 minutes. There were no differences between the \[S II\] 6716 and \[S II\] 6731 position-velocity diagrams, so we combined these to produce a single \[S II\] spectrum. The \[N II\] 6548 line is fainter by a factor of three than the companion line \[N II\] 6583, and the fainter line is also contaminated by faint residuals from a bright night sky emission line from an adjacent order, so we simply use the 6583 line for the \[N II\] line profiles.

Internal Dynamics of HH 110
---------------------------

The image in Fig. 15 divides the position-velocity diagram into ten distinct emitting regions along the slit. Spectra for each of these positions appear in Fig. 17 for H$\alpha$ and for the sum of \[N II\] + \[S II\]. All regions have well-resolved emission line profiles in H$\alpha$, \[N II\], and in \[S II\]. Only object 9 showed any difference between the \[S II\] and \[N II\] profiles, with \[N II\] blueshifted by 12 km$\,$s$^{-1}$ relative to \[S II\].

In low-excitation shocks like HH 110, the forbidden line emission peaks when the gas temperature is $\sim$ 8000 K [@hartigan95], which corresponds to a spread in radial velocity owing to thermal motions of HWHM = ((2ln2)kT/m)$^{0.5}$, or 2.6 km$\,$s$^{-1}$ for N, and 1.7 km$\,$s$^{-1}$ for S. These thermal line widths will be unresolved with the Kitt-Peak observations, which have a spectral resolution of 11 km$\,$s$^{-1}$. Therefore, the observed widths of the forbidden lines measure nonthermal line broadening in the jet. This line broadening most likely arises from nonplanar shock geometry or clumpy morphologies on small scales, as the HST images show structure down to at leas