It's amazing how ancient pens occasionally produce an innoivation that would have revolutionised the industry had they taken it a little bit further. In this case MacNiven and Cameron devised a filling system that was only a tiny bit removed from an Aerometric filler. Had they seen the natural improvement they would have jumped ahead about forty years, missing out button fillers and lever systems altogether.
The pen was the 'Cameron', a hard rubber, Gold nibbed affair:
The pen shown is missing the filler bars at the moment but the arrangement can be seen in a c.1912 advert for the pen:
All that was needed was to link the bars at the top and free one side at the bottom and you have an aerometric system, but they didn't, and the idea died for a few decades.
Nevertheless, it is a wonderful pen, I look forward to completing the restoration.