Outstanding discussion everybody!!!! It is extremely fascinating to read the well explained and supported observations here concerning the feasability of these weapons features. While edged weapons were in themselves primarily simple in thier dynamics, it is amazing how very complex their actual use and construction became. While the sliding weight feature discussed here remains purely conjecture found in literature thus far, many other interesting features are well established in developed examples, such as the thumb rings brought up on a concurrent thread and both hilt and blade shapes and construction.
It would appear that the sliding weight feature remains a figment of literary imagination as no existing examples have been seen, and such features are not mentioned in contemporary narratives or material describing edged weapons.
The mercury filled channel blades, while early examples seem to remain somewhat in question, the concept seems to have been applied in some latter examples of weapons, with this likely to be in response to the earlier tales of such weapons. An illustration of this occurs in at least one 'Bowie' knife produced in the 1860's with a hollow channelled blade containing mercury. Whether it was ever used is not described, however by its appearance (published in "The Bowie Knife", Norm Flayderman) it seems an extremely clumsy weapon.
As this excellent discussion continues, I remain hopeful that in some hidden corner of some archives or museum we will find evidence of the sliding weight on some long forgotten sword. I'm confident that if such a sword can be found it will be by the members and readers here!!
Meanwhile, the comprehension of physics and dynamics has always eluded me, but you guys make it understandable!!! Thank you so much!!
All the best,