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629.]
PRATICAL UNITS.
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with the additional statement of the particular fundamental units on which they are founded.
When very large quantities are to be measured, a large unit is formed by multiplying the original unit by one million, and placing before its name the prefix mega.
In like manner by prefixing micro a small unit is formed, one millionth of the original unit.
The following table gives the values of these practical units in the different systems which have been at various times adopted.
| Fundamental Units. | Pratical System. | B.A. Report, 1683. | Thomson. | Weber. |
| Length, | Earth's Quadrant, | Metre, | Centimetre, | Millimetre, |
| Time, | Second, | Second, | Second, | Second, |
| Mass. | 10-11 Gramme. | Gramme. | Gramme. | Milligramme. |
| Resistance | Ohm | 10⁷ | 10⁹ | 10¹ |
| Electromotive force | Volt | 10⁵ | 10⁸ | 10¹¹ |
| Capacity | Farad | 10⁻⁷ | 10⁻⁹ | 10⁻¹⁰ |
| Quantity | Farad (charged to a Volt.) |
10⁻² | 10⁻¹ | 10 |
