Lectures on Select Subjects in Mechanics, Pneumatics, Hydrostatics, and Optics, Plate XIX


“Plate XIX” features eight figures to accompany the text entitled “Of Optics.” Figure 1 illustrates the manner in which light travels through a multiplying glass to the eye. Figure 2 diagrams the optical physics of the portable box camera obscura with a mirror to right the inverted image. Figure 3 illustrates the physics of the common looking glass. Figure 4 explains the optical illusion of reduced proportion in a looking glass. Figure 5 illustrates the separation of light into the color spectrum through a glass prism. Figure 6 is a diagram of the color spectrum of light on a wheel. Figures 7 and 8 are small geometric diagrams mapping the movement of light rays in the illusion of an arched rainbow.

Primary Works: 

Lectures on Select Subjects in Mechanics, Pneumatics, Hydrostatics, and Optics

Accession Number: 

Thordarson T 1061

Height (in centimeters): 


Width (in centimeters): 


Marks Description: 

Inscr. top left “Plate XIX”; lower left “J. Ferguson, delin.”; and lower right, “J. Mynde Sc.”

Printing Context: 

“Plate XIX” of twenty-three folded plates appears in Lectures on Select Subjects, first edition. This version of Lectures on Select Subjects is bound with Astronomy Explained upon Sir Isaac Newton’s Principles and Made Easy for those who have not Studied Mathematics, Third Edition (1764), and A Supplement to Mr. Ferguson’s Book of Lectures on Select Subjects in Mechanics, Pneumatics, Hydrostatics, and Optics, with the Use of Globes, The Art of Dialing (1767).

Associated Events: 

James Ferguson (1710–1776) was elected a fellow of the Royal Society of London in 1763. On April 1, 1764, Ferguson observed the eclipse of the sun from Liverpool, England, about which he wrote a paper for the Royal Society entitled, “Observations on the eclipse of the sun” that same year (P. Rothman, “Ferguson, James” Oxford DNB).

Associated People: 

Ferguson's text is based on the scientific work of Sir Isaac Newton.

Astronomy Explained was dedicated to the Earl of Macclesfield, Viscount Parker of Ewelme in Oxfordshire, and Baron of Macclesfield in Cheshire.

The text Lectures on Select Subjects was dedicated to Prince Edward.

Associated Places: 

The Royal Society of London.

Associated Texts: 

Astronomy Explained published in 1756 (1st ed.) and reprinted in 1757 (2nd ed.), 1764 (3rd ed.), 1770 (4th ed.), 1772 (5th ed.), 1778 (6th ed.), 1785 (7th ed.), 1790 (8th ed.), 1794 (9th ed.), 1799 (10th ed.), (P. Rothman, “Ferguson, James”).


The camera obscura portrayed here is an excellent example of Ferguson’s interest in the physical properties of the scientific problem at hand. Instead of illustrating a portable box camera obscura with a cut-away side view to reveal the inner mechanisms of lens and mirror, Ferguson, the delineator of the plate, does away with the outer form of the device completely and diagrams instead the physical pathway of an image through the camera obscura.


Optics, light, lenses, camera obscura, looking glass, prism, color spectrum


The text in Lectures on Select Subjects was drawn from James Ferguson’s extensive public lectures on a variety of scientific topics. A self-taught scientist and a Fellow of the Royal Society, Ferguson sought to elucidate both his texts and his lectures for easy comprehension by his public. Ferguson said, “I had a view … to avoid all superfluity, and to render everything as plain and intelligible as I thought the subject would admit of” (qtd. in P. Rothman, “Ferguson, James" Oxford DNB). His sentiments align with concurrent popular interests in science as a rational and edifying recreation, exemplified in texts by M. Guyot, William Hooper, and Jacques Ozanam, and by the serial public lectures given by Ferguson, Joseph Priestly, and other natural philosophers. According to Jessica Riskin, these lecturers’ “efforts to amuse were dramatically successful. Fashionable people thronged to see nature’s ways laid bare” in the late eighteenth century (J. Riskin, “Amusing Physics” 43). The intention of this type of public lecture was to be both didactic and amusing, rather than tediously difficult or boring; further, “an insistence on simply seeing permeated the amusing physics curriculum,” an impetus which parallels the copious illustration accompanying this type of text in the eighteenth and nineteenth centuries (J. Riskin, “Amusing Physics” 45). Ferguson, however, did not shy away from the mathematical complexities of these topics in either his lectures or his texts, nor did he necessarily suggest experiments for the amateur scientist to perform at home. Rather, an understanding of the figures on “Plate XIX” and the associated text from Lectures on Select Subjects requires a high level of scientific and visual literacy.

In this plate, Ferguson diagrams the path of an image (AB) through the camera obscura: the image moves through the glass lens (CD) and is inverted (GH) and then reflects off the glass mirror (EF) and is righted (JK). The careful attention to the optical physics of the apparatus, rather than its outward appearance or construction—especially when considered with both the repeated printings of the text and the general popularity of Ferguson’s lectures—suggests a more complex engagement with and understanding of optics on the part of the public in the Romantic period. Moreover, the absence of the recognizable physical structure of the camera obscura in the form of a box or room on “Plate XIX” subverts Jonathon Crary’s generalizing contention that the apparatus disembodies and interiorizes vision (J. Crary, Techniques of the Observer 39). Without the structure of the camera obscura apparatus in which to obscure oneself, the optical physics of the device supersede any potential effects of disembodiment or interiorization of vision.


A textbook on the subject of optics.


Crary, Jonathan. Techniques of the Observer: On Vision and Modernity in the Nineteenth Century. Cambridge, MA: MIT Press, 1990.

Ferguson, James. Lectures on Select Subjects in Mechanics, Pneumatics, Hydrostatics, and Optics with the Use of Globes, The Art of Dialing, and The Calculation of the Mean Times of New and Full Moons and Eclipses. London: Printed for A. Millar, 1764.

Riskin, Jessica. “Amusing Physics.” Science and Spectacle in the European Enlightenment. Ed. Bernadette Bensaude-Vincent and Christine Blondel. Burlington, VT: Ashgate Publishing Company, 2008. 43-64.

Rothman, Patricia. “By 'The Light of His Own Mind': The Story of James Ferguson, Astronomer.” Notes and Records of the Royal Society of London, 54.1 (Jan., 2000): 33-45.

---. “Ferguson, James (1710–1776).” Oxford Dictionary of National Biography. Ed. H. C. G. Matthew and Brian Harrison. Oxford: OUP, 2004. Online ed. Ed. Lawrence Goldman. Oct. 2007. 19 Mar. 2009 http://www.oxforddnb.com/view/article/9320.

Stafford, Barbara Maria. Artful Science: Enlightenment, Entertainment, and the Eclipse of Visual Education. Cambridge, MA: MIT Press, 1994.

--- . “Revealing Technologies/Magical Domains.” Devices of Wonder: From the World in a Box to Images on a Screen. Ed. Barbara Maria Stafford and Frances Terpak. Los Angeles: Getty Publications, 2001. 1-115.

Long Title: 

James Ferguson, Lectures on Select Subjects, Plate XIX: Optical physics and instruments, copper plate engraving, 16.8 x 17.5 cm, inscr. top left “Plate XIX,” lower left “J. Ferguson, delin.,” and lower right, “J. Mynde Sc.,” Thordarson Collection, UW Department of Special Collections.