and Astronomical Notices. 177 



thorny mazes of difficulty and of perplexing doubts, where so 

 many of our fathers laid down and died ; while we, the fortu- 

 nate inheritors of the results of their toilsome labours, may 

 look back, at an early age, upon all those obstacles over- 

 come, and find ourselves in a position to grapple at once with 

 arcana of nature, still bound up in the shadowy future. 



Under, such circumstances, the pendulum experiment of 

 Foucault, starting on the easily demonstrated principle, that 

 the plane of vibration of a simple pendulum is independent 

 of any smooth and equable motion either of translation or 

 rotation of its point of support, and shewing that the appa- 

 rent change of the direction of the plane of vibration of such 

 a pendulum, as compared with any ^xed object on the earth, 

 is the consequence really of the latter' s motion of translation 

 and rotation. Such a capital experiment was received with 

 the greatest enthusiasm by all thinking men. 



One man, however, there is, who, having recently written 

 a work to prove that the earth stands still, and that the sun 

 is only two feet in diameter, was not a little put out by the 

 recent discoveries ; and has got up an experiment to prove, 

 dogmatically, that the world does not rotate ; and it must 

 be allowed that the legion of experimenters who have started 

 up to repeat and to testify to Foucault's experiment, have 

 offered the enemy too many weak points which might 

 reasonably be attacked. 



Now, though the principle involved may be perfectly sound 

 in itself, still in trying it practically, many errors may arise, 

 and render it as difticult for the multitude to repeat, as the 

 daguerreotype fixation of the images of the camera obscura, 

 or some of Dr Young's beautiful and paradoxical experiments 

 on the interference of light. 



Mr Airy, therefore, has been of great service to the cause, 

 by stepping out in his peculiarly clear and practical manner, 

 and demonstrating in a paper read at the Royal Astronomical 

 Society of London, what effect will follow from a pendulum 

 not describing a straight line exactly, which no free pendulum 

 can do perfectly, but an oval not differing very much there- 

 from. And he shews that if a pendulum 52 feet long (which 

 performs its double vibration in 8 seconds), vibrates in an 

 ellipse whose major axis is 52 inches and minor axis 6 inches, 



VOL. LI. NO. CI, — JULY 1851. M 



