Many thanks for the input from members various, but my thinking on this water level scheme would be to measure temperature difference by using an enclosed volume of some liquid (oil or wax etc.) Lets not lose sight of the fact that there were not the electronic facilties back in 1906 (the year of the Morriss) and the Morriss brothers were "practical" men with engineering backgrounds related to there knowledge at 1906 and before.
In approaching a solution to this Pressure gauge level indicator problem we must bear in mind the facilities available in "their day", I would not be interested in fitting some super electronic device on my car, but would consider the "Morriss scheme as it is reported as fact in a contemporary report written by Mr. Frank Morriss,and he did in fact say "travelled many thousands of miles" with a device such as this (pressure gauge) .
On a more practical level it would be much easierto convert temperature fluctuations than pressure fluctuations, we do this all the time with the automatic by-pass valve, I see an enclosed system with some sort of "tuning" device to accomodate maximum pressures without blowing the gauge up. I will venture into this scheme at some point in the future but for now I am boiler building for the Pearson-Cox, please keep up the input it is quite interesting

Thanks Kelly I read the article with interest and quite understand the "thinking" behind the idea, it is of a simial nature to my way of thinking and will at some point be tried on the Pearson-Cox, the parts are made and will be fitted during the boiler installation.
My experiments with this type of gauge (water level/press.g.) have shown great promise with a closed system and a hydraulic "tuning" cushion, it is small and light weight but requires a "sender" with an increased volume of oil rather than simply a tube, this would reflect the long tube mentioned in the article, of course a long tube could be incorporated by coiling, and would probably be more responsive but for now my bench tests are satisfactory, if and when the thing is up and running I will offer the results in an article in our magazine,
Thanks for your input regards Les