I was just reading William and Ceil Baring-Gould's sadly under-Annotated Mother Goose, in which rhyme #274 is:
Characteristically, the Baring-Goulds footnote the literal meaning of "ell," but are completely silent on the tougher meaning of "yard." (And never mind trying to explain the nonsense syllables!)
I'm vaguely familiar with the concept of a "yard of ale" — Wiktionary says it's "The amount of ale that fills a very tall tapering beer glass (approximately 1 yard)," not that that really narrows it down if you don't provide the width of the glass too. Wikipedia says roughly 1.4 liters.
I found this reference from John Taylor's 1639 A Juniper Lecture:
... a bowle of pottage that holds a Gallon, and a Barly bagge pudding of a yard long, and some Bull Beefe ...
and this reference from John Shipp (1840):
I was exceedingly hungry ... I longed for a slice ... [Finally, Shipp and the plum-pudding woman] agreed that in consideration of a quarter of a yard of pudding and a shilling, to be to me paid and delivered, my new shoes were to be handed over to the dealer in plum pudding, as her own proper goods and chattels. This contract being honourably completed, I retreated [to eat his quarter-yard of pudding in a single sitting "without any great exertion."]
I'm also vaguely familiar with the idea of a boiled pudding, in the Christmas-pudding sense, but I thought those were typically ball-shaped. I'm tempted to guess that a "plum-pudding dealer" might well use a long skinny bag to make it easier to portion out slices, and that a "yard of pudding" would just be a three-foot slice from one of these long skinny pudding-sausages... but is that right?
Looking for some historical context to connect the dots here. How precise of a measuring unit is this "yard"? How much hunger would be sated by a quarter-yard of plum pudding? Can anything besides ale and pudding be measured in "culinary yards"? :)
EDITED TO ADD: The nursery rhyme that kicked this all off is of the genre that the Baring-Goulds call "self-evident propositions." Commenter YosefBaskin points out that the nursery rhyme might be saying that just as a tailor's "goose" is not a member-of-the-category "birds," similarly a puddingwise "yard" is not a member-of-the-category "units of length"! However, I think it's equally reasonable to read it as saying that self-evidently a tailor's "goose" won't fly, and (independently) self-evidently a yard of anything is not as much as an ell of the same thing. It's not necessarily an exact parallel with the preceding line. (Trust me, I've read enough of these rhymes this week to know they're not all paragons of parallel construction! ;))