When customers like Samuel Pepys visited the shop of Thomas Tuttell, instrument maker to the king, they could purchase a pack of mathematical playing-cards. The seven of spades, reproduced as Figure 1, depicted the diverse connotations of magnets, or loadstones. These cards cost a shilling, and were too expensive for many of the surveyors, navigators and other practitioners shown using Tuttell's instruments. They provide an early example of the products promising both diversion and improvement which were increasingly marketed to polite audiences. Tuttell's description of loadstone as ‘a treasure of hidden vertues’ encapsulated many contemporary perceptions of these naturally occurring magnets which were to endure throughout the century. This phrase, with its hints of concealed financial and epistemological benefits, resonates with major eighteenth-century analytical themes, such as commercialization, the opposition between vice and virtue, and the fascination with the occult in the face of Enlightenment rationality. This card is emblematic of the multiple interpretations and utilizations of magnetic phenomena during the eighteenth century. It thus provides a useful starting-point for exploring some of the disputes which arose as enterprising individuals concerned with natural philosophy promoted themselves, their activities and their products.

In the overwhelmingly public world of the twentieth century, science often seems simultaneously remote and ubiquitous. There are many complex reasons for this, of course, not the least being the capacity of technology for material transformation and the apparent inability of scientific discourse to communicate its practice to the unanointed. In some ways, our current predicament appears similar to that of the late eighteenth century when so many promises had already been made of what natural philosophy might accomplish, and when many clamoured for access to the power of natural philosophical practice. At that point, on the verge of the stunning dislocations of the industrial revolution, many of the literate and mechanical public took considerable steps to bridge the gap otherwise policed by social distinction.

How may scientific research contribute effectively to industrial development? This question has been debated for many years. However, a recent development in this discussion has come from a number of eminent scientists and others who have become concerned with what has become known as the public understanding of science. According to them, a greater understanding of science by members of the public would result in a higher value being placed on scientific research, which, eventually, would result in both increased social status for scientists and growing funding from government and industry for their work. Thus, in part, concern about the public understanding of science is an indirect way of influencing the outcome of discussions about the science budget.

A quotation from J. T. Desaguliers, one of the foremost scientific lecturers in England until his death in 1744, contrasts the use of demonstrations to show physical principles and those designed to imitate real situations:

I have indeed a Machine with brass wheels whose steel axes have very small pivots nicely made that any of the wheels set in motion will turn for the space of more than half an hour… but the use of my machine being chiefly to show how near these kinds of experiments may be brought to agree with a mathematical theory; we cannot expect that any carriage to bear weight can have so little friction. Therefore I choose to relate Monsieur De Camus's Experiments made on Models of Carriages of an inch to a Foot every way representing Carts and Waggons… because it shows us directly what is the real Friction in the carriages at present in use.

Viewed in the light of the discussions of scientific lecturing in eighteenth-century London contained in this issue, the case of medicine may be said to be both more of the same but also something different.