What is the title of Isaac Newton's book on optics?

Isaac Newton’s book on optics is titled Opticks. Its full original title was Opticks: or, A Treatise of the Reflexions, Refractions, Inflexions and Colours of Light.

Newton published the first English edition in 1704. The book grew from his investigations of prisms, lenses, thin films, diffraction, and the composition of white light. Unlike the mathematically formal Principia, Opticks presents a large collection of experiments, observations, demonstrations, and speculative questions about the nature of light.

The unusual spelling with a final “k” reflects the title Newton used, so Opticks is the canonical answer even though modern science generally spells the subject optics. A Latin translation appeared in 1706, and later English editions expanded Newton’s famous “Queries,” which explored topics ranging from heat and electricity to the possible relationship between matter and light. The book helped make experimental optics central to scientific debate in the eighteenth century.