above

matter to the censure of the Reviewer. But I hope my remarks will lead him to suppose, that I could defend my " philosophical language," in many instances wherein, from the nature of the subject, it may appear very exceptionable. His strictures thereupon, I nevertheless receive with great respect, and a desire to keep them in view: Sincerity and candour are eminently manifest in them; and I court the continuance of such correction.

In the first impression of the foregoing letter, I omitted to remark, that any supposition of visible lines HAVING breadth (although refuted above, and although if tenable it would be of no consequence to the "LAWS OF VISION,") is however a supposition that could only embrace all those Visible Lines occasioned by our looking at colors spread upon one same continuous surface, such as the objects on a Painting, or a Writing. ALL OTHER visible lines (which are infinitely the more ordinary and more numerous objects) defy every pretence to suppose that they have any visible breadth; because, it is manifest, for instance, that the color of my hand, when I hold it up to the light, cannot run into the color of the sky which does not touch my hand by several miles; and therefore such lines can have no breadth in themselves; far less, then, can we see in them what they have not.

This last kind of lines is what I gave for Examples, in the original broaching of the subject: and it was quite gratuitous my choosing to defend, as I still do, the first kind, also.

A

LETTER

ON

THE TRUE PRINCIPLES

OF

ADVANTAGEOUS EXPORTATION.

IN REFUTATION OF CERTAIN POPULAR NOTIONS ON

THAT SUBJECT.

SECOND EDITION.

LONDON:

ADVERTISEMENT.

THE Editor of the following Letter lays it before the Public in the same form he received it, unaltered, except in some few trifling verbal corrections. He conceives that by so doing, he best fulfils the intention of his late friend, the Author. The concluding passages are omitted, being on a somewhat different topic, and too desultory for publication.`

A LETTER,

&c. &c.

I HAVE not leisure, at present, for the work you wish me to undertake; and cannot, without much pain and difficulty, separate my thoughts on a general subject, and bring forward only such portions of them as bear on some particular branch of it: but, as I every day see, more and more, the importance of setting in a right point of view the principles of profitable trade, I will endeavour to pick out, and put together in a connected manner, those observations I have so often made to you on that subject, in the garden at L, and leave it to your discretion either to publish them as I deliver them, or (by first applying your taste and skill to the materials) to build them up into some handsomer form.

I recollect the difficulty you had in believing that so simple and elementary a principle, and one so important in its application, should have escaped the attention of the writers on political economy; and now that so many years have elapsed, and these topics have been so often since discussed, I should not be at all surprised if in fact my ground be already taken possession of. Well; you live in the busy world-look into the pamphlets and dissertations of the day, and see if there be any tolerably clear exposition of my principle already before the public: if there should, suppress the observations I now send you. For myself, I have not yet seen anything that tends to clear up the mist which has hung over these points.

I will first refresh your mind with a sketch of some of those erroneous opinions (as I call them) that are to be met with every day; and then endeavour to state and illustrate the true principle. You will find the same things here that we have so often talked