Oh, great, just what I needed: pictures of terraced houses in Lancashire. It's an interesting link, though.
Here's a possible xplanation, from xrefer:
spinning jenny
A machine, patented (1770) by Hargreaves, for spinning a number of threads simultaneously.


It extended the principle of the spinning wheel by carrying several spindles (ultimately 120) vertically - the idea is said to have come to Hargreaves when he saw a spinning wheel, knocked over by his daughter Jenny, fall on its side. In the 1780s the spinning jenny began to be superseded by the mule for spinning cotton, but its adaptation to wool ensured its survival well into the 19th century.


Market House Books Dictionary of British History, © Market House Books Ltd 1987
My father always called a female mule a jenny.