ScientificAmerican1915-03-13.jpg Scientific American 1915-03-06 Back-Cover AdThumbnailsScientific American 1915-03-20Scientific American 1915-03-06 Back-Cover AdThumbnailsScientific American 1915-03-20Scientific American 1915-03-06 Back-Cover AdThumbnailsScientific American 1915-03-20Scientific American 1915-03-06 Back-Cover AdThumbnailsScientific American 1915-03-20Scientific American 1915-03-06 Back-Cover AdThumbnailsScientific American 1915-03-20

The large transit circle at the Paris Observatory, now used only for obtaining accurate time.