560 The Ile\'. S. Haughton on the Theory of Sound. 



perpendicular to the table. The result will be, therefore, that 

 the line of vibration will appear to revolve round in the plane of 

 the table. 



But with what angular velocity ? To explain this, we refer 

 again to our original illustration. The question is, How much 

 has that shilling revolved about its owai centre in the time that 

 the earth has taken to make half a revolution ? The centre of 

 the shilling has traversed the half of a parallel of latitude ; but 

 the face of that shilling, which has always been looking north- 

 ward, has not evidently turned half round ; that is, if the centre 

 of the shilling had been fixed, the face would not have made so 

 much as half a revolution about its centre. In fact, the shilling 

 would have tm-ned round just as much as if that semi-parallel of 

 latitude had been taken off the globe and disposed as a thread 

 upon a plane table in the form of a circle, with that fixed point 

 in the globe^s axis to which we have alluded as centre, and the 

 shilling had then been made to move along the thread, with its 

 face always turned to that centre. This thread would not form 

 a complete semicircle. 



Indeed the angle moved through by the plane of vibration in 

 twelve hours is proportional to the angle subtended at the fixed 

 point in the earth's axis to which we have alluded, by the semi- 

 parallel of latitude laid out into a plane circle ; it is therefore 

 proportional to the length of that semi-arc by radius, or to the 

 sine of the angle between the north horizontal line and the axis 

 of the earth, that is, proportional to the sine of the latitude. 

 Hence the time of a complete revolution is obtained, as beforcj 

 by dividing twenty-foui" hours by the sine of the latitude. 



LXXXII. On Professor Potter's Theory of Sound. 



■iivj. ''.. £?/ Me iJev. Samuel Haughton. o.,; 



"'"Tb" Me Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IN Professor Potter's answer to my remarks on his Theory of 

 Sound, he has expressed his surprise at my ignorance of the 

 atomic constitution of matter, but appears to have overlooked 

 the fact that my argument was ad hominem, and that I was not 

 stating my own views on the subject. 



On reading carefully Prof. Potter's theoiy, as he has stated it 

 in the February Number of the Magazine, I (in common with 

 many others) put a construction upon his meaning which ap- 

 peared to be a fair representation of his views, and from that 

 construction I deduced the conclusion that the introduction 

 of atoms in that sense did not alter the equations of motion. 

 This conclusion, it appears from the May Number of the 



