Essays on Philosophical Subjects

Essays on Philosophical Subjects, by the Scottish economist Adam Smith, is a history of astronomy until Smith's own era, plus some thoughts on ancient physics and metaphysics.
This work was published posthumously, in 1795, using material which Smith had intended to publish but had not prepared at the time of his death in 1790. This was done by his literary executors, two old friends from the Scottish academic world; physicist/chemist Joseph Black and pioneering geologist James Hutton. A brief account of their work appears in a section entitled 'Advertisement by the Editors'.
The book consists in distinct works:

The History of Astronomy
The History of the Ancient Physics
The History of the Ancient Logics and Metaphysics
Of the External Senses
Of the Nature of that Imitation which takes place in what are called The Imitative Arts

The History of Astronomy is the largest of these and is thought to have been written in the 1750s, before Smith's major works. The overall understanding is excellent, though the Glasgow Edition of 1976 includes some detailed criticism of his use of sources. It also defends him for calling Newton a philosopher rather than a scientist; the word 'scientist' did not exist before 1839.
The History of Astronomy is divided in four sections.

Section I : "Of the effect of Unexpectedness, or of Surprise".
Section II : "Of wonder, or of Effects of Novelty".
Section III : "Of the Origin of Philosophy". Here Smith defines Philosophy as a rational explication of the world.
Section IV : "The History of Astronomy". Smith outlines the history of modern astrometric systems. He appoints : Copernic, Gallilee, Kepler, Descartes, and Newton system. The modern astronomy is no longer mathematical but of the physical order. According to Smith, if a system is simpler and more efficient in its explanations, then it is more likely to be closer to the way nature works.

It also contains Smith's first mention of the invisible hand:

"Of the External senses" deals with each sense in turn. According to Smith, each idea is an expression of a sensory impression. He concluded the previous section intituled "The History of the Ancient Logics and Metaphysics" on the question of language. The language motif is continued.

Touching
Tasting
Smelling
Hearing
The order of passage is not insignificant. Smith affirmed that every sens expect touching is directly linked to an organ. Usually, seeing is the sens that is the more mobilised. Indeed, he has a value of true, clarity and knowledge.
In this part of the essay, two philosophical debates are mobilised :

The distinction between the primary and secondary qualities.
The Molyneux problem.