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break it muft a& with greater advantage; and as the weight of adherent bodies equal- ly ftrong increafes much fafter than their length*, the fhorter beam will be equally ftrong and much lighter at the fame time. The longer beam, however, has one ad- vantage over the fhorter, which is, that it contributes more to make the motion fteady, and this it does by being a longer lever. Any extraordinary interruption muft put all the parts of the plough in fome mea{ure

* Similar folids, and fuch only can be equally ftrong, are to one another as the cubes of their lengths.[Euclid b. 12. prop. 2. M¢ Laurin’s account of Sir I. Newton, p.170.] Suppofe two bodies, whofe lengths are as 2 and 3. The cubes ofthefe numbers, are 8 and 27-_ Which laft num- bers, if the bodies are of the fame kind of matter, will exprefs their different weights. Hence it ap- pears, if the length of a body be increafed only in the proportion of 2 to 3, its quantity of matter muft be augmented fo much, to make it equally{trong as be- fore, that its weight becomes three times and near a half greater. This is the reafon that the larger a- nimals of a kind are not ftronger in proportion to their fize than the fmaller, becaufe their quantity of matter does not increafe fo faft as their bulk. Ifit did, they would be rendered perfeétly unwieldy and a burden to themfelves.