For an idea of what the sentence of hard labour would have involved in Victorian Britain, see http://gallery.e2bn.org/gallery812-vcp.html

Mark, I hadn’t thought of that. Perhaps a clue would be in the fact that the warehouse where Martin went to purchase the oil was that of Thomas, Fripp, and Thomas, who, I find by Googling, were soap makers. That implies animal oil, doesn’t it, most likely the whale oil you suggest?

And, as usual, some detail completely unrelated to the central point of the story piques my curiosity. Because of the date (1854), it is a near certainty that the oil was not a petroleum distillate. Was it whale oil? Or coal oil? And what was the price of those oils in the 1850s, and how might that have affected the seriousness of the crime?

Speaking of crime, and its punishments, Mr. Martin’s timing was propitious–had he committed the theft 25 years earlier, he would have been subject to the death penalty upon conviction. Or to what may have been worse, transportation (to Australia)!