Portrait of Agnes A M Yair, dated 21 April 1870, by Alexander Brothers, Glasgow
I was wondering whether it could actually be 1878, but the style would suggest the earlier date.
And now positively identified by a family member (see comments below).
One of 140 images from a fascinating album. For more information see the full set
Just how many more of these images can we identify, and what can we find out about the people they portray?