14 



On Pendulum Observations. By Alexander Gerard, Esq., 



Aberdeen. 



Gordon's Hospital, 

 Aberdeen, 20th April 1853, 



Sir, — Having read in the last number of the Edinburgh 

 New Philosophical Journal an account of Observations on the 

 Pendulum in Bunker's Hill Monument, and an article respect- 

 ing the Ordnance Survey, I take the liberty of sending you a 

 description of an apparatus erected by me upwards of two 

 years ago, which exhibited the phenomena since observed in 

 America. 



On the 12th of January 1851, a pendulum was suspended 

 in the following manner : — The ring B was fixed near the 

 the top of the west wall of a room. 

 Into this was hooked a copper wire? 

 which was brought down over the 

 end of abeam, CD. This beam was 

 built of four pieces of deal, in the 

 form of a rectangular spout (with 

 a view of obviating the effects of 

 hygrometrical changes), and rest- 

 ed against the wall on a pivot at D. 

 A block of granite, weighing about ™" 

 one cwt., was attached to the end of the wire. As the ring 

 at B projected a little over the point D, the apparatus was 

 in the condition of a gate swung upon a post not quite ver- 

 tical. When set a- vibrating, it was seen to perform one oscil- 

 lation in about 15 seconds, which shewed that it had the same 

 amount of defiexibility as a pendulum hung freely from the 

 height of 630 feet. The position of the weight was noted 

 on a table placed near to the outer end of the beam ; and, 

 if not at rest (which it seldom was), it was either steadied 

 by the hand, or the middle of the small vibration was taken. 

 It was observed to be subject to a daily variation, hanging 

 farthest south about 8 or 9 in the morning, and farthest 

 north about 3 in the afternoon. After its movements had 

 been watched for some weeks, the apparatus was dismount- 

 ed, and fixed on the north wall of the room. The weight 

 would thus obviously be free to move in the east and west 



