prie’ (says he) ’ceux qui voudront les repeter, s’ils n’ont pas le temps de mesurer les resultats apres plusiers jours d’un travail continu, d’observer les ouvriers a differentes reprises dans la journee, sans qu’ils sachent qu’ils sont observes.  L’on ne peut trop avertir combien l’on risque de se tromper en calculant, soit la vitesse, soit le temps effectif du travail, d’apres une observation de quelques minutes.’  Memoires de l’Institut. vol.  II, p. 247.  It frequently happens, that in a series of answers to such questions, there are some which, although given directly, may also be deduced by a short calculation from others that are given or known; and advantage should always be taken of these verifications, in order to confirm the accuracy of the statements; or, in case they are discordant, to correct the apparent anomalies.  In putting lists of questions into the hands of a person undertaking to give information upon any subject, it is in some cases desirable to have an estimate of the soundness of his judgement.  The questions can frequently be so shaped, that some of them may indirectly depend on others; and one or two may be inserted whose answers can be obtained by other methods:  nor is this process without its advantages in enabling us to determine the value of our own judgement.  The habit of forming an estimate of the magnitude of any object or the frequency of any occurrence, immediately previous to our applying to it measure or number, tends materially to fix the attention and to improve the judgement.

Section II

On the domestic and political economy of manufactures

Chapter 13

Distinction Between Making and Manufacturing

163.  The economical principles which regulate the application of machinery, and which govern the interior of all our great factories, are quite as essential to the prosperity of a great commercial country, as are those mechanical principles, the operation of which has been illustrated in the preceding section.

The first object of every person who attempts to make any article of consumption, is, or ought to be, to produce it in a perfect form; but in order to secure to himself the greatest and most permanent profit, he must endeavour, by every means in his power, to render the new luxury or want which he has created, cheap to those who consume it.  The larger number of purchasers thus obtained will, in some measure, secure him from the caprices of fashion, whilst it furnishes a far greater amount of profit, although the contribution of each individual is diminished.  The importance of collecting data, for the purpose of enabling the manufacturer to ascertain how many additional customers he will acquire by a given reduction in the price of the article he makes, cannot be too strongly pressed upon the attention of those who employ themselves in statistical enquiries.  In some ranks