Astronomical Lectures read in the Chapel of Harvard College at Cambridge in America, 1780-1781 Digital

Lecture 1, On the certainty, usefulness and ease of mathematical science, was delivered at a Harvard assembly on May 10, 1780, and subsequently read in 1784 and 1786. This lecture is an explanation of Enlightenment ideals regarding reason, science, and the pursuit of knowledge; it was the first lecture Williams gave at Harvard as Hollis Professor.

Lecture 2, On a very uncommon darkness which took place in the New England States, May 19, 1780, was read on June 7, 1780. This lecture describes what was widely called the "Dark Day"; Williams believed the darkness had resulted from an abnormal accumulation of vapors in the atmosphere. Modern research shows that the "Dark Day" was likely caused by wildfires burning in Canada.

Lecture 3, On Astronomy: the figure and dimensions of the Earth, was first read on Sept. 20, 1780 and again in 1784 and 1786.

Lecture 4, The appearance and situation of the heavenly bodies, was first read on October 4, 1780 and again in 1784 and 1786.

Lecture 5, The truth of the Copernican system, was first read on February 21, 1781 and again in 1784 and 1786.

Lecture 6, Spots in the Sun; his rotation round his axis, and atmosphere, was first read March 14, 1781 and again in 1785 and 1787.

Lecture 7, The fixed stars: their appearance, magnitude and constellations, was first read September 12, 1781 and again in 1784 and 1787.

Lecture 8, The fixed stars: their catalogues, representation by planispheres and globes, and the method of finding them, was first read on September 19, 1781 and again in 1785 and 1787.

Lecture 9, Changes in the fixt stars, with conjectures as to the cause of these phenomena, was first read on October 10, 1781 and again in 1785 and 1787.

Lecture 10, Double and cloudy stars, lucid spots, the milky-way, the zodiacal light, the stars probably suns, was first read on November 21, 1781 and again in 1785 and 1787.

Lecture 11, The parallax, magnitude, and distance of the fixt stars, is incomplete and has no indication of being read.