Photos of the Allais Paraconical Pendulum

Here are some decent scans of the only photographs that seem to be available of the Allais Paraconical Pendulum apparatus. Of course, as per usual, you can store these pictures on your computer by right clicking them. If you print them each filling its own page, they look very decent.

The only thing you can't see clearly in these pictures is the all-important support ball, or "bille" as Allais calls it. This consisted of a commercial SKF ball bearing of 6.5 mm diameter, claimed to be "high precision". By modern standards this was not high precision at all; my metrological contacts tell me that the ball was likely about grade 100, i.e. accurate to 100 millionths of an inch. Allais used a new support ball for each fourteen minute swinging episode, in an attempt to average out the errors due to inaccuracies of the balls, of which he was well aware. The ball rolled upon the support plate labeled S in the fourth and last figure (about which Allais tells us nothing), and was held in a conical depression in the (non-labeled) cylindrico-conical mount shown as projecting downward from the bracket E. So the entire pendulum was supported upon this little ball. The idea (a brilliant one) was to eliminate sliding friction and to have no friction except rolling friction.


Back to the website main page.