In her paper called "Eighteenth grammars and book catalogues", Anita Auer quotes Feather (1985:34) on the popularity of Dyche's Guide to the English Tongue: between 1733 and 1747, 33 editions came out of the work, to a total of 265,000 copies, "or nearly 18,000 copies a year, of which a mere handful is extant".

ECCO includes 15 editions and reprints of Dyche's Guide to the English Tongue, form the 2nd edition of 1710 down to a 102nd edition published in 1800. Thisis a phenomenal record, comming close to that for Lindley Murray's grammar of 1795. Though Dyche had died in the 1720s, his name still appears on the title-page of this late edition, so it must have acted as an important selling device at the time. Google Books even includes a reference to a reprint dated 1821, which shows that the book contintued to be popular well into the nineteenth century.

These figures make those which I discussed for the publication history of Lowth's grammar (Tieken-Boon van Ostade 2008) seem very insignificant indeed: there, I argued that down to the early 1780s one and often two editions or reprints came out of his grammar every year, in a printrun of a thousand copies each. This seemed like an innovation in the field of grammar publishing, until I encountered the figures quoted for Dyche.

But Dyche's Guide to the English Tongue is not a grammar (which also explains why Alston does not list it in Volume 1 of his bibliography) but a guide on pronunciation. The author evidently used the word tongue in a narrower sense, i.e. as referring to speech, not language (see OED, s.v. "tongue" ), than for instance Brightland and Gildon in their Grammar of the English Tongue (1711) (see Buschmann-Goebels 2008). Still, it is interesting to see that a guide to pronunciation was so popular throughout the eighteenth century. Dyche did publish a proper grammar as well, in 1732. However, Alston notes that no copy was ever located: he found that it was merely announced in the London Magazine of that year.

Reference: for the papers by Auer, Buschmann-Goebels and myself, see Ingrid Tieken-Boon van Ostade (ed.), 2008, Grammars, Grammarians and Grammar Writing in Eighteenth-Century England, Berlin/New York: Mouton de Gruyter.