The following information is paraphrased from an essay by Bengt Johnsson in the excellent edition of 22 sonatas by Galles, published by Institut d'Estudis Catalans, Societat Catalana de Musicologia, Barcelona 1995.
The composer Josep Galles is not mentioned in the majority of dictionaries such as EITNER, Quellen- Lexicon and Die Musik in Geschichte und gegenwart. The Diccionario de la musica (Labor, 1954), edited by H. Angles and J. Pena, gives the following information on this Catalan composer: 1758-1836, was born in Castelltercol and died in Vic, a town to the north of Barcelona. He was organist and cathedral choirmaster at Vic. However, little of his music has been published. In the Arxiu Musical de Montserrat there is a collection of his Versos for organ, and in the Biblioteca de Catalunya in Barcelona, there is a manuscript (BC 388) containing 23 sonatas for keyboard by Galles. [...]
The sonatas of Galles are much more ambitious than those of other Catalan composers of the period. It is difficult to say exactly when they were composed. Some were written for the new hammer-action piano (piano-forte). Others, with their many ornamental notes, sound equally good on a harpsichord, for which they were probably written.
The style of Galles is relatively simple and free of superfluous ornamentation. The melody is often present in broken octaves, a technique which is typical of the hammer-action piano.
The manuscript from which these sonatas are taken is unbound and not in very good condition; it is small, unclean and unclear. The many abbreviations and repeat symbols make it difficult to read.
My own observations: Galles appears to have two styles. One is Scarlatti-like, and some of the pieces written in this vein are excellent; they have a good rhythmic pulse and are not too demanding on either player or listener. They have effective modulations, sometimes to surprising keys. The ornamentation, as ever, should be regarded as a guide, not as a rigid model, and extra ornamentation can be added where required, especially on repeats. Some of the sonatas are not so good (e.g. no.4) - there is sometimes a lack of pulse caused by over-fussy rhythms and a lack of tonal direction.
The second style is more Mozart-like, but the melody lines are completely different. There is no real counterpoint, unlike the "Scarlatti"-type sonata and there is often a rapid broken-chord bass a little like that of Alberti, but the figures are more awkward and often contain repeated notes. Sonatas 22 and 23 are examples of this type. To be effective the performance must be fluent, confident and polished. [...]
Source: Nigel Deacon: Josep Galles Sonatas accessed 11 September 2007