error in postscript -- unknown family 'Arial'

Hi,

I am a new R user and am trying to run another person's data analysis
script that is failing with the following:

Error in postscript("Fig.eps", FALSE, "Arial", width = 13.83,  :

  unknown family 'Arial'


I am running with Mojave 10.14.4 if that matters. Any help would be much
appreciated!

Thanks!

-ryan