Early photoelectric cells and, later, Charge-Coupled Devices (CCDs) began to replace film, allowing for direct, accurate, and quantitative measurement of light intensity across the spectrum. The earliest picture of a spectrometer I have found is this cut from Hauksbee and Whiston's Course of Lectures, ca. There was much. His instrument employed a small aperture to define a beam of light, a lens to collimate it, a glass prism to disperse it, and a screen to display the resulting spectrum. This first spectroscope was nearly in modern form.
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