Evidence for a significant secular decrease of the solar diameter has recently been presented by Eddy and Boornazian (1979). With regard to the enhanced interest in periodic or non-periodic variations of figure and size of the Sun, a very reliable series of 129 transit observations made by Tobias Mayer in 1756 1760 has been analyzed. The necessity for applying adequate corrections to measurements of this kind is stressed again. Mayer's observations yield R ☉ = (960.16±0.13)″. This is in excellent agreement with more recent photoelectric transit observations and lends no support whatsoever to the assumption of a secular decrease.