The inventory of the material in the Gabinete de Física of the University of Coimbra set up under the Pombaline reform began with an account of the "machines" designed for the study of the general properties of matter. Professor dalla Bella's textbooks on Physics also opened with this topic, after the usual preliminaries.

The requirement to present the general properties of matter ahead of the systematic study of physical phenomena forced the author to declare at the outset his philosophical attitude to the ideas current at the time. Taking such a stand corresponded, in the 18th century, to a fighting position based upon an interpretative system which was always, no matter what the position taken, an easy target for attack. The general properties of matter discussed in dalla Bella's textbook were extent, divisibility, impenetrability, porosity, and inertia. Of these, divisibility immediately posed the question of acceptance or rejection of the theory of the existence of atoms, certainly one of the most controversial and heated issues of the day.

The philosophical attitude of physicists in the 18th century in respect of this and other factors, may be vividly captured by the work of Father Teodoro de Almeida, one of the most famous Portuguese pedagogues. His work Recreasaõ Filozofica (Philosophical Recreation) is couched in the style often used in 18th century educational works, where various individuals speak as though they were actors in a play, some contesting and others defending certain principles. There are three protagonists in the Recrasaõ: Teodósio, "a modern philosopher" who is Teodoro de Almeida himself; Eugénio, who wants to know who is right, be they Ancient or Modern, and to whom the arguments are therefore directed; Sílvio, a doctor friend of Teodósio, well educated and trained in Aristotelian philosophical thought. The three engage in a protracted debate about the nature of the Universe, animals, plants, heavenly bodies, Logic, and Metaphysics.

"All things", Teodósio says, "have two parts, which the Philosophers call Principles; which are Matter and Form."

"In what, then, lies diversity?" asks Eugénio the disciple interested in the conversation. Teodósio explains that opinions diverge "when we speak of what this matter physically is, and its form". "This matter, of which all things are composed, is an aggregate of such incredibly small corporeal parts that each one separated from the others would be completely invisible: it is beyond imagination; it is impossible to have any idea how small are these parts of matter, into which bodies are divided. One grain of sand could be divided into more than a thousand parts". (p. 13)

Sílvio responds with the words of the ancient philosophers: "[...] we do not contradict this, we defend otherwise that an Angel could divide grain of sand for all eternity, and never fail to divide it. The Moderns have more problems with this, because they say that these particles, or smallest parts of matter, cannot be divided further and they call them Atoms, whence comes the name, Atomists. This doctrine is as fantastic and subtle as most of the ones they believe in." (page 24) The discord between the Ancients and Moderns in respect of the divisibility of matter is thus put in these terms: for the Ancients, matter could be divided indefinitely; the Moderns held that there was a limit to the division of matter, which is the atom.

The battle lines were thus drawn between the Scholastics and the Moderns. They all thought that matter was divisible but the Scholastics and some Moderns (Cartesians) saw no end to the dividing process; other Moderns thought that divisibility ended with the atom (Newtonians and Gassendians). Moderns believed that the constituent parts of matter, whether atoms or not, were arranged in a particular way that gave the form in which they appeared. The Scholastics, however, held that the form was regarded as an entity, an entity that was distinct from matter.

Impenetrability is another general property of matter according to which, as was said, a body could not occupy a space already occupied by another. The doubts that were raised among the ancient physicists as to the existence of this property related to fluids. They knew that solids were impenetrable; but that liquids, and, more especially, gasses, could also be so, provoked argument.

For the "modern" philosophers of the 18th century, all matter was essentially solid. Liquids and gases gained their fluidity from the greater or lesser scarcity of their constituent solid parts. The smallest particles of matter are themselves always solid. Thus, all matter is solid and this solidity explained its impenetrability. To be solid and impenetrable became synonymous.

The experiments that "modern" physicists in the 18th century carried out to convince their students of the impenetrability of matter had, therefore, two purposes: 1) to prove that the constituent particles of liquids and gases are solid; 2) to prove that a body can only occupy the place of another once the latter has been removed.

The third group of "machines" in the Pombaline Gabinete de Física were used to study the "porosity" of matter, enormously important in 18th century Physics and Chemistry.

Physicists of the age resorted to the concept of pores to explain a great many phenomena, such as dissolution, certain chemical reactions, density of substances, etc. The pore notion was, in that century, as significant as the electron has been in ours.

The concept of inertia, its causes and consequences, motion, acquired velocity, variations in velocity, life force, the quantity of motion, centrifugal force, were the object of heated controversy between physicists and theologians.

"Inertia", says Teodoro, "is the incapacity of voluntary movement". Such incapacity, he stresses, means that "the matter is inert, that is, unable to change the state [of being at rest or in motion] in which it finds itself" (ibid, II, 114). "Every body placed at rest remains motionless until an outside cause makes it move." " Every body placed in motion remains moving until an outside cause puts it at rest." (II, 145).

"Every moving body persists in its line of movement until an outside cause makes it change its line." "Every moving body persists in the same degree of velocity until an outside cause reduces or increases it" (II, 146).

Teodoro made the effort, with all his customary clarity, to make it understood that the inertia of a body has nothing to do with its weight, and to prevent the confusion that could easily arise. "There are some", he says, "who do not wish to admit any resistance to a body at rest except that which gravity produces" (II, 155), and he demonstrated experimentally that there was no good reason to think in this way.

The Pombaline Gabinete de Física only has two instruments from the original collection that were used for studying the general properties of matter: one was to study impenetrability (instrument 1); the other to illustrate porosity (instrument 3). We have included the diving bell in this section (instrument 2), although it was acquired at a later date, because its functioning was also based on the property of impenetrability and it does appear in this section in the 1851 catalogue.