When the first stamps of the (soon-to-be) Victorian Colony went on sale on Thursday, 3rd January 1850, the same man who designed and produced those stamps - Thomas Ham - was also called upon to manufacture the first obliterators at the same time. This was to ensure the stamp could not be used again for postal purposes. Because of their design, these obliterations came to be known as "Butterflies"; and over the years these first stamps, and the cancellations, have become highly prized by collectors.

BUTTERFLY 15 of GEELONG

At the time of their issue there were 36 Post Offices operating in what was still the Port Phillip District of New South Wales, and these obliterators, along with other office "furniture", were allocated along the various 'Lines of Road' which radiated out from the main settlement - Melbourne, which was (naturally) allocated number "1".

Thomas had been commissioned to make 50 Butterflies, to allow for the expected increase in the number of Post Offices over the next few years.

http://www.adb.online.anu.edu.au/biogs/A040373b.htm