76 Kotes on a Ghronograpkic ApparaUis. 



After this brief glance at the methods ah-eady adopted or 

 proposed for obtaining uniform rotation, I will now return to 

 the more special subjects of these notes. 



At the subsequent meeting of our Section A the question 

 of uniform rotation was discussed, and Mr. Kernot suggested 

 Huyghens' Parabolic Pendulum as a governor, and submitted 

 a plan for its construction. Now, Huyghens' pendulum 

 was invented 200 years ago, and is theoretically a perfect 

 governor ; but with the exception of a rough imitation of 

 the principle in a steam-engine governor I could not find 

 that it had ever been used or even tried. I determined, 

 however, to adopt Mr. Kernot's suggestion, and try this 

 governor. At first the results gave me no encouragement, 

 and I almost determined to give it up, more especially as I 

 imagined that there must be some almost insuperable prac- 

 tical difficulty in the way to account for so old and theoreti- 

 cally perfect a '' governor" never having been adopted. How- 

 ever, by a little perseverance and alteration of form of 

 pendulum, I arrived at better results, and eventually suc- 

 ceeded in getting a pendulum constructed which is almost 

 practically perfect, and the performance of which has with- 

 stood far more trying tests than it would be subjected to in 

 practice. Huyghens' Parabolic Pendulum therefore has in 

 my hands given the closest approximation to uniform rota- 

 tion ever yet, I believe, obtained; and that with a mechanism 

 so simple and easily constructed as to put all the more 

 elaborate but less effective forms in the shade. 



While in England last year I read a paper to the Koyal 

 Astronomical Society on " Some Experiments with Huyghens' 

 Parabolic Pendulum," but was not able to show one in 

 operation. I can now do so, and that is my excuse for 

 bringing it under your notice this evening. In the paper 

 referred to I gave the principle of construction I had adopted, 

 and the conditions I had found necessary to secure success. 

 It is nevertheless, I think, desirable to give a brief descrip- 

 tion of the pendulum in this place, more especially as I have 

 the whole apparatus in working order before you. 



This chronograph apparatus is not very different from the 

 ordinary forms, and is styled a " barrel chronograph," because 

 the registration takes place on paper covering a barrel which, 

 by reason of the perfect governance of the pendulum, 

 revolves precisely once in a minute, while a syphon pen, 

 actuated by an electro magnet, makes a mark on the paper 

 every second, as the current from a galvanic battery is 



