I have posted some resources related to Margaret Cavendish’s Philosophical Letters.
The Letters in the Philosophical Letters. This document gives some information about the letters that make up Margaret Cavendish’s Philosophical Letters (London, 1664). The descriptions of each letter are in a small number of categories: number, topic, reference, and note.
Some of the Philosophical Letters. This page presents a handful of the letters in Margaret Cavendish’s 1664 Philosophical Letters. They are letters 1, 4, 30, 35, and 36 of part 1.
Philosophical Letters, 1.1-29 (pdf). This is a modernized version of the early part of Margaret Cavendish’s 1664 Philosophical Letters: the front matter, and the first 29 letters in part 1. Most of those letters (4-29) discuss the work of Thomas Hobbes. The text has been modernized in its spelling, use of capital letters, and use of italics. Few changes have been made to Cavendish’s punctuation, the main one being to add apostrophes indicating possession.