[Phys-L] a counterintuition: please examine

[Brian Whatcott <betwys1@sbcglobal.net>]

BC said in part:
//
> In my previous post (the second, this is the third) I explained the added mass was done W/the pendulum stopped. 
>
>   Note: experimentally extremely difficult, however, here are some methods. 
>
>
> 1,  the support is absolutely rigid (added mass will affect the operation if not rigid)
> 2,  mass may be added by changing the bob’s metal (from brass to tungsten W/the same size, etc.)  so dissipation the same.
>
> Note:  there is a problem if the result is as I predicted, the dissipation will change W/ the reduced amplitude.  Can be compensated by changing the atmosphere causing > the dissipation, As I wrote very difficult to do experimentally. 
>
>   3 and more; I think one will now understand what I’ve attempted.
//
This is not quite the third BC contribution on the topic of pendulum QHe cited amplitude reduction if the bob's mass is increased as a Huygens observation, which he mentioned about fourteen years ago. (6/9/2007)The  air pressure surrounding a pendulum is comparatively easy to reduce with an evacuated column; the basis of the Shortt-Metronome clock (although domestic sources prefer to mention the Hall-Littlemore Clock which featured a quartz oscillator in the loop as THE most accurate - if noisy -  pendulum)
  I assert that the pivot however ALWAYS sees increased dissipation with increased bob mass, so I prefer to state BCs #2 proposition like this:"Air drag is reduced at reduced amplitude. It follows that a postulated reduction in pendulum amplitude with increased bob weight is due to increased dissipation at the pivot point." 
This leitmotif later pulled in a contribution from Hugh, the keeper of the Trinity clock. (Eight years later in 2015!) If I have not previously mentioned it, I note that the son of the then keeper of Big Ben told me that this pendulum was regulated seasonally by the addition or subtraction of a penny from the top of the bob which effectively shortened or lengthened it respectively.