Letter, from Henry Oldenburg to John Hecker, dated at London Thanks for sending his printed notices about the observation of the next transit of Mercury across the sun in 1674; concerning discrepancies between the Boulliaud and Caroline tables - that the transit will be observable from Britain in the former and not according to the latter; concerning John Flamsteed's views on Rudolphine calculus and Boulliaud tables 27 February 1673