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The following communications were read : 



I. Supplement to the "Account of Pendulum Experiments 

 undertaken in the Harton Colliery;" being an Ac count of 

 Experiments undertaken to determine the correction for the 

 Temperature of the Pendulum. By G. B. AIRY, Esq., 

 Astronomer Royal. Received February 13, 1856. 



(Abstract.) 



Adverting to the circumstance that, in the Harton Experiment, 

 there was a mean difference of 7 between the temperature above and 

 below, and that a careful determination of the coefficient for tem- 

 perature-correction was therefore necessary, the author describes the 

 process by which the correction was now investigated by experiment 

 on the same pendulums which were used in the Harton Experiment. 

 Two rooms were selected at the Royal Observatory, Greenwich, 

 having firm stone floors, and admitting of being heated, one by a 

 stove in the room, the other by a hot-air-apparatus below. One 

 pendulum was mounted upon its iron stand, with clock and other 

 apparatus, in one room, and the other in the other room. Care was 

 taken that the pendulums and their thermometers should be effec- 

 tually protected from radiation. The two clocks were compared by 

 carrying a chronometer from one to the other, and remarking the time 

 of coincidence of beats ; a method which admits of very great accu- 

 racy, when (as in this instance) the distance through which the 

 chronometer is to be carried is small. In the Fifth Series (counting 

 the series in sequence to those of the Harton Experiment), Pendulum 

 1821 was kept in heat, and Pendulum 8 cool, and continuous obser- 

 vations were kept up during forty hours. In the Sixth Series, Pen- 

 dulum 8 only was kept in heat, and observations were again kept 

 up during forty hours. The Seventh and Eighth Series were similar, 

 respectively, to the Fifth and Sixth. The temperatures are referred 

 to two of the thermometers used in the Harton Experiment, and to 

 two other thermometers supplying the place of two of the Harton 

 thermometers which cannot be found. The observations were con- 



