333. The effect of machinery in printing other periodical publications, and of due economy in distributing them, is so important for the interests of knowledge, that it is worth examining by what means it is possible to produce them at the small price at which they are sold. 'Chambers' Journal', which is published at Edinburgh, and sold at three halfpence a number, will furnish an example. Soon after its commencement in 1832, the sale in Scotland reached 30,000, and in order to supply the demand in London it was reprinted; but on account of the expense of 'composition' it was found that this plan would not produce any profit, and the London edition was about to be given up, when it occurred to the proprietor to stereotype it at Edinburgh, and cast two copies of the plates. This is now done about three weeks before the day of publication--one set of plates being sent up to London by the mail, an impression is printed off by steam: the London agent has then time to send packages by the cheapest conveyances to several of the large towns, and other copies go through the booksellers' parcels to all the smaller towns. Thus a great saving is effected in the outlay of capital, and 20,000 copies are conveyed from London, as a centre, to all parts of England, whilst there is no difficulty in completing imperfect sets, nor any waste from printing more than the public demand. 334. The conveyance of letters is another case, in which the importance of saving time would allow of great expense in any new machinery for its accomplishment. There is a natural limit to the speed of horses, which even the greatest improvements in the breed, aided by an increased perfection in our roads, can never surpass; and from which, perhaps, we are at present not very remote. When we reflect upon the great expense of time and money which the last refinements of a theory or an art usually require, it is not unreasonable to suppose that the period has arrived in which the substitution of machinery for such purposes ought to be tried. 335. The post bag despatched every evening by the mail to one of our largest cities, Bristol, usually weighs less than a hundred pounds. Now, the first reflection which naturally presents itself is, that, in order to transport these letters a hundred and twenty miles, a coach and apparatus, weighing above thirty hundredweight, are put in motion, and also conveyed over the same space. (2*)