Abstract
The word ‘periodical’ immediately calls to mind huge stacks of bound volumes neatly arranged on library shelves. Yet, in historical terms, it would be hard to claim that ‘periodical’ is a word endowed with a definite and univocal connotation. Even the criterion of ‘periodicity’ leaves a lot out of account. Forms historically assumed by periodicals often envisaged regular schedules of appearance, but this was often more of a wish than a reality. Thus, great care needs to be taken in accepting at face value the dating of issues and volumes. Scientific periodicals, whether purely professional or purely commercial (and the many forms in between), existed in given historical circumstances and had to compete with different and alternative forms of publication which were also issued in instalments (especially dictionaries and encyclopaedias). They were not the only or even the preferred vehicle for a scientist to communicate or engage in debate. The role of the reading public, in science as well as in many other matters, was never one of a passive receiver: during the long nineteenth century, in several countries, readers claimed the right to intervene in scientific debates, and favoured publications that appeared to accommodate their demands.