We present HST /GHRS echelle observations of multiple interstellar lines of \ion C1 , \ion Mg1 , \ion Cr2 , and \ion Zn2 towards both stars in the \mu Cru binary system .
Despite large differences in the profiles of the neutral species , no significant variations between the stars are seen in the \ion Cr2 and \ion Zn2 line profiles .
In particular , the \ion Zn2 absorption observed at -8.6 km/sec towards \mu Cru is constant despite greatly enhanced columns of the neutral species at this velocity towards \mu ^ { 1 } Cru .
An analysis of the fine-structure excitation of \ion C1 in this cloud implies that the density is n _ { H } < 250 cm ^ { -3 } .
From the lack of variation in the ( optical ) \ion Na1 D2 line profiles towards \mu ^ { 1 } and \mu ^ { 2 } Cru in spectra taken 21 months apart , we can place a lower limit to the size of the structures of \sim 10 AU .
These results are discussed in the context of recent radio and optical studies of apparently pervasive high density small-scale interstellar structure .