436 Mr. Scrymgeour's Experiments to determine the Irtfluencc 



Set, No. 7. 



r, . Gain in Extent of 



Experiments. g4 Hours. Vibration. 



In air + 12-3 8 . 2-23° 



In exhaustion, 6j in. -f 11*6 2-36 



Ditto 13i ... +9-2 2-36 



Ditto 15^ ... +7*6 



In air +7*0 2-23 



Ditto + 5'6 2-23 



Ditto + 5*5 2-23 



Ditto +5-1 2-23 



Ditto +4-2 2-23 



Ditto + 4-7 2-23 



In exhaustion, 8 in. . . + 7'4 2*35 



Ditto 16| +7*3 2*35 



This set of experiments is not very satisfactory, owing to the 

 change of rate occasioned by the weakening of the suspending 

 spring. The difference between the results of the experiments 

 in air and in exhaustion is small, being only about 2*5 seconds 

 for nearly the same extent of vibration ; whereas the results of 

 those in air ought to have been about 6*5 seconds slower. 



This discrepancy may be accounted for, by attributing a 

 small portion of it to the effect of the scapement, and the rest 

 to the strength of the suspending spring, which caused the 

 pendulum to return more quickly, when at the limit of the 

 vibration, than if it had been weaker. The difference between 

 the extents of vibration in air and in exhaustion is only *14 of 

 a degree, which would make no difference in the times of the 

 vibration, as the spring was adjusted. 



In the above experiments the maintaining power was 5 

 pounds ; now, with the same pendulum vibrating on a knife- 

 edge, it would require only 2\ pounds to cause the pendulum 

 to vibrate to the same extent ; consequently, in the former case, 

 the power employed was double what was necessary to produce 

 the effect. This power being applied to the pendulum, had 

 the effect therefore of bending up the suspending spring, which 

 would thus have more power in its return in the first incre- 

 ments of descent, and would be less retarded by the current, 

 than when vibrating on a knife-edge. 



As the spring would cause the pendulum to return more 

 quickly from the highest point in the arc of vibration, it might 

 be supposed that the vibrations would be performed in a less 

 time, or that they would be the same as those of a shorter 

 pendulum. This is so far the case, that the pendulum must 



