This beginner's guide is useful background to how the art of astrology was taught in the 1790s. There are no signs to suggest it was written by Gilbert so I have not included it in his list of contributions to the Magazine.
The Gentleman who desires directions in the pursuit of astrological knowledge, is directed first to make himself competent in Astronomy; then he may consult the following books, in order: Ball's, Thresher's, Blagrave's, or Bishop's Introduction to Astrology, or all together, as one will explain what the other will not obviate so clearly. Lilly's Christian Astrology, Salmon's Soul of Astrology, Ramsay's Astrologia Munda, Coley's Key new filed, Eland's Tutor; and last, though not least of all, Partridge's Defectio Geniturarum, proving the old principles superior to the modern. Upon particular parts he may consult Gadbury's Astrological Seaman for nautical affairs; Sanders upon Sickness; but the best upon diseases, is Culpeper's Astrological Judgments, the whole of which is reprinted, and prefixed to the new edition (now publishing at Mr Locke's) of the Family Physician.[...]
Mercutio requires our opinion of the "Illustration of Astrology". To this we answer, that, we only esteem it a quack performance, very unequally executed, by a head incompetent to the task of either composing or compiling; for in it we discover all the blunders of old John Gadbury, introduced without correction or distinction, in the very language of Bedlam.