On an improved optometer for estimating the degree of astigmatism and other errors of refraction / by John Tweedy.

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On an improved optometer for estimating the degree of astigmatism and other errors of refraction / by John Tweedy. Public Domain Mark. Source: Wellcome Collection.

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This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.