Leng, Dr Loh Wei; Keong, Khor Jin (19 September 2011). "Mad Ridley and the rubber boom". Malaysia History. Archived from the original on 27 July 2013. Retrieved 9 February 2013.
Leng, Dr Loh Wei; Keong, Khor Jin (19 September 2011). "Mad Ridley and the rubber boom". Malaysia History. Archived from the original on 27 July 2013. Retrieved 9 February 2013.