Transvaal 1905 British Association Commemorative Postmark

1905 BRITISH ASSOCIATION JOHANNESBURG: Transvaal KEVII 1d postcard to Austria showing the rare special commemorative postmark in violet. This postmark used for only FOUR DAYS is dated on the FIRST DAY 28TH AUGUST 1905 amongst the few examples known, is the earliest recorded. F-VF, rare.
The 75th Annual Meeting of the British Association for the Advancement of Science was held in South Africa, with meetings held in the main centres. Special datestamps were provided for postmarking mail handed to the secretary. For Johannesburg a temporary post office was opened in the Technical Institute from 28th August to 1st September.