title_body: What are the true origins of the yard of ale?
upvoted_answer: I found a blog post where the author has (most thoroughly, in my opinion) gone in search of some primary source of evidence for the origins of the yard glass. Unfortunately, they seem to have turned up nothing definitive.
  
  On one point, the post is quite consistent: there isn't any real evidence to suggest that the story of the stagecoach or mailcoach driver drinking from the yard-glass is true. 
  
  It mentions sources on the history of glassmakers:
  
  
    The same absence of evidence occurs in specialist books on drinking glasses. The history  of the Worshipful Company of Glass Sellers, published in 1898, has a drawing of the Eton  “long glass”, but no coach drivers.
  
  
  And also the history of coaches:
  
  
    Specialist books on coach travel also fail to supply references to coach drivers and ale-yards.
  
  
  The coach explanation appears to be wholly made-up:
  
  
    The earliest reference to the coach driver legend I have found is from 1952
  
  
  And, inferring from previous evidence provided by the author, this is almost a century after coach travel has been superseded by steam trains.
  
  The author also makes an interesting point; a coach driver was almost certainly not handed a yard of ale from the alehouse window, because the risk of breaking the glass (which would have been expensive) was too great!
  
  Most of the evidence of the post tends to suggest that the yard of ale was originally intended as a bit of a joke, and attempting to drink the whole thing without spilling a drop was a fun game to play.
  
  
    When air reaches the bulb it displaces the liquor with a splash, startling the toper, and compelling him involuntarily to withdraw his mouth by the rush of the cold liquid over his face and dress.
  
  
  To summarise, in one final quote from the most-excellent article:
  
  
    But with all that, I hope you’ll agree, we have found no evidence that
    the yard of ale was originally “designed to meet the needs of
    stagecoach drivers” in a hurry. In fact, there is no evidence that the
    yard of ale was ever used to refresh coach drivers at all (and if it
    had been, it certainly wouldn’t have been handed up to the driver
    through an inn window, which would be an excellent way to either spill
    the ale or smash the glass). Instead, I think, it seems clear that the
    yard of ale was (1) produced as something of a show-off, for the
    glassmaker and the owner, and (2) primarily or almost solely supplied
    and bought as a “forfeit glass”, for use in drinking games and
    contests of skill, just as it is today.