Mb. Edmuio) Htint on RotaJtory Motion. 201 



March 10, 1858. — Mk. Bbtce, Vice-President, in the Chair. 



The following papers were read, with illustrations, by the President: — 



" On the Interference of two adjacent Organ Pipes tuned to the same, 

 or nearly the same, note." 



" On the Vibrations of Rotating Bodies." 



Mr. Hunt exhibited an experiment illustrative of his paper " On 

 Rotatory Motion;" but in consequence of the lateness of the hour, 

 deferred till next meeting reading Notes in continuation of that paper. 



March 24, 1858. — The Pkesidenx in the Chair. 



Mr. John Dickie and Mr. John Dougan were elected members. 



Mr. Hart described some appearances of the EcHpse of the Sun on 

 the 15th, which were not generally seen by observers in this quarter. 

 Mr. Hart was fortunate enough to catch a momentary glimpse of the 

 sun's disc at the completion of the phenomenon. 



Mr. Edmund Hunt read, and illustrated by experiment, Notes in 

 continuation of his paper on Rotatory Motion, which was brought before 

 the Societv on the 2d of December last. 



Additional Notes on Rotatory Motion. By Ediiund Hunt. 

 AVhe>' a peg top spins on a point which experiences friction upon the 

 supporting surface, that friction will cause the top to rise if inclined, 

 and with the greater rapidity the blunter the point is. This effect 

 takes place by means of a tendency to accelerate the top's precessional 

 motion. Supposing the top to be spinning in an inclined position upon 

 a horizontal surface, the friction tends to make the peg roll along that 

 surface, and this tendency acts as a rectilinear force tending to carry 

 the top bodily along in a direction such that, if it moved fast enough 

 the point would roll instead of rubbing on the surface. This rectilinear 

 pressure being apjilied to the point of the peg, instead of the top's 

 centre of gravity, causes such a translation of the toj) combined with a 

 I'otation about its centre of gravity, that its peg moves in advance. 

 Consequently, supposing the top to be at first inchned up towards the 

 north, and its point to move towards the west, it will in a short time 

 be inclined up towards the east. The rolling action will then tend to 

 can-y the top towards the north, and after a second interval it will be 

 inclined up towards the south, and so on. In other words, the top 

 describes a circle, and is inclined in towards the centre thereof So far 

 the precessional action is not taken into account. Supposing the top 

 Vol.. IV.— No. 1. 2d 



