Identifier: s1philosophicalmag58londuoft (find matches)
Title: The Philosophical magazine; a journal of theoretical, experimental and applied physics
Year: 1798 (1790s)
Authors:
Subjects: Physics
Publisher: London Taylor & Francis (etc.)
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: Ontario Council of University Libraries and Member Libraries

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mallmotion in the two little balls, and their connecting rod, two otherlarge balls, of ten inches diameter, are connected together bycertain machinery, at like distance as the former, and capa-ble of being moved to different distances, or positions, on thehorizontal level with the small balls. By so setting the largeballs near the small ones, these are attracted by the former, pro-ducing a very small motion in them, and in consequence a veryslow vibration. So minute are these motions, that the extentof the vibrations is but a small fraction of an inch, and the dura-tion of each vibration is not performed but in the time of severalminutes, from 3 or 4 to near 15 minutes. So minute are thesemotions, that telescopes and other means are necessary toview and to estimate their quantity and durations. To producethese minute motions, very complex machinery is necessarilyemployed, while the delicate movements are watched for manyhours together, during many days, and recorded with regard to the
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On the Mean Density of the Earth. 9 the extent and time of each vibration. Then, from these spacesand times, the density of the earth is to be calculated, by peculiartheorems, as compared with the vibrations of common pendulums,that are produced by the attractions of the earth. AH these effects were so minute, and produced by machineryso complex, and the results calculated by theorems derived fromintricate mathematical investigations, that it is impossible at first,for ordinary readers, to conceive how any accurate results can bededuced from them, and even for the more judicious reader toplace confidence in them, except chieHv on account of the highcharacter of the experimenter himself. From the nature of lY.tmachinery I could therefore derive no confidence in the resuhs,nor compare them with the mountain experiment, without re-peating the whole of the calculations. But, after a long life spentin almost daily abstruse investigations, from the tenth year of myage, and now being at 84,s1philosophicalmag58londuoft

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