Most of the text of the Letter is incorporated in the text of Christian Morals.
The text of this on-line edition is a reproduction of a facsimile edition published in 1924 as No. 1 of "The Hazelwood Reprints", London. The following information supplied with the 1924 text is of interest and use:
NOTE
THE original edition of Sir Thomas Browne's Letter to a Friend printed as a folio pamphlet in 1690, after his death, is of extreme rarity. The preservation of the few examples that exist seems to be due to their having been bound up with other tracts or at the end of copies of the collected edition of his Works published in 1686, as was the case with the one used for this reprint, kindly lent us by Mr. P. J. Dobell. Simon Wilkin in his well-known edition of Browne states that he had only seen one copy, that in the British Museum (643 L.24 (6) ). It appeared for a second time in Browne's Posthumous Works printed for Curll in 1712. The present edition is a line for line reprint of the first, the spelling and punctuation having been exactly adhered to except in the places given below.
[These alterations are noted in the on-line version as notes.]
The alterations are necessary to the sense of the passages in which they have been made, and the errors were doubtless due tot he printer. With the one exception mentioned these alterations have the support of Dr. Greenhill.
The form "s" has been substituted for long ess throughout the text.
Page numbers are indicated as anchors in the HTML source, so that you may travel (approximately) to a page by appending "#page3", "#page4" etc. to the URL: thus page 12 is http://penelope.uchicago.edu/letter/letter.html#page12 (or letter/index.html#12, depending on how you got here). (Page 1 is the title page and page 2 is its [blank] verso; they are not up yet.) When a word breaks over a page break, it is indicated as a comment in the HTML source. The original marginalia are reproduced in a separate file, with links to the HTML text. Additional notes are also in that file, marked in [ ] square brackets.