During the 1761 transit of Venus, the Russian scientist Mikhail Lomonosov observed a ring of light around the planet. Lomonosov attributed the ring to the refraction of sunlight, which he correctly hypothesized was caused by the atmosphere of Venus. Further evidence of Venus' atmosphere was gathered in observations by Johann Hieronymus Schröter in 1779.[78] The planet also offered Alexis Claude de Clairaut an opportunity to work his considerable mathematical skills when he computed the mass of Venus through complex mathematical calculations.[79]