impeded by the friction that would arise from the slightest deviation in any of the bearings.
(323.) In conducting experiments upon machinery it is quite a mistake to suppose that any imperfect mechanical work is good enough for such a purpose. If the experiment is worth making, it ought to be tried with all the advantages of which the state of mechanical art admits; for an imperfect trial may cause an idea to be given up, which better workmanship might have proved to be practicable. On the other hand, when once the efficiency of a contrivance has been established, with good workmanship, it will be easy afterwards to ascertain the degree of perfection which will suffice for its due action.
(324.) It is partly owing to the imperfection of the original trials, and partly to the gradual improvements in the art of making machinery, that many inventions which have been tried, and given up in one state of art, have at another period been eminently successful. The idea of printing by means of moveable types had probably suggested itself to the imagination of many persons conversant with impressions taken either from blocks or seals. We find amongst the instruments discovered in the remains of Pompeii and Herculaneum, stamps for words formed out of one piece of metal, and including several letters. The idea of separating these letters, and of recombining them into other words for the purpose of stamping a book, could scarcely have failed to occur to many: but it would almost certainly have been rejected by those best acquainted with the mechanical arts of that time; for the workmen of those days must have instantly perceived the
