in general upon the length of time before they reach a bearing state and during which they afterwards continue in it.  If this certain proportion happens at any time to be disturbed the produce must become irregular.  Thus, if at any period the number of bearing vines shall be found to exceed their just proportion to the total number, the produce at such period is to be considered as above the mean, and a subsequent decrease may with certainty be predicted, and vice versa.  If then this proportion can be known, and the state of population in a residency ascertained, it becomes easy to determine the true medium number of bearing vines in that residency.

There are, agreeably to the form of the survey book, eleven stages or classes of vines, each advanced one year.  Of these classes six are bearing and five young.  If therefore the gardens were not liable to accidents, but passed on from column to column undiminished, the true proportion of the bearing vines to the young would be as six to five, or to the total, as six to eleven.  But the various contingencies above hinted at must tend to reduce this proportion; while, on the other hand, if any of the gardens should continue longer than is necessary to pass through all the stages on the survey-book, or should remain more than one year in a prime state, these circumstances would tend to increase the proportion.  What then is the true medium proportion can only be determined from experience, and by comparing the state of a residency at various successive periods.  In order to ascertain this point a very ingenious gentleman and able servant of the East India Company, Mr. John Crisp, to whom I am indebted for the most part of what I have laid before the reader on this part of the subject, drew out in the year 1777 a general comparative view of Manna residency, from the surveys of twelve years, annexing the produce of each year.  From the statement it appeared that the proportion of the bearing vines to the whole number in that district was no more than 5.1 to 11, instead of 6 to 11, which would be the proportion if not reduced by accidents; and further that, when the whole produce of the twelve years was diffused over the whole number of bearing vines during that period, the produce of one thousand vines came out to be four hundred and fifty-three pounds, which must therefore be estimated as the medium produce of that residency.  The same principle of calculation being applied to the other residencies, it appeared that the mean annual produce of one thousand vines, in all the various stages of bearing, taken collectively throughout the country, deduced from the experience of twelve years, was four hundred and four pounds.  It likewise became evident from the statements drawn out by that gentleman that the medium annual produce of the Company’s settlements on the west coast of Sumatra ought to be estimated at twelve hundred tons, of sixteen hundred weight; which is corroborated by an average of the actual receipts for any considerable number of years.