Weighing the Earth

As in all other scientific systems of taking measurements, especially those in which the object of measurement is not directly comparable with our established units, special instruments have to be constructed by which certain measurements are taken, these serving us by the aid of the known laws involved with sufficient data to make calculations from which we derive the answer sought.
This necessitates the selecting of a method out of the possible many at our disposal, which, with the same degree of care taken in those measurements, will lead, all things considered, to the most reliable result.
The less the number of such measurements, and the larger the parts measured (the size of a part here refers to it as a multiple of the smallest portions of it capable of measurement), as a rule, the more dependable must be the result.