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"The Nicholson hydrometer of constant volume is a hollow cylinder carrying at its lower end a basket, d, heavy enough to keep the apparatus upright in water. At the top of the cylinder is a vertical rod carrying a pan, a, for holding weights, etc. The whole apparatus must be lighter than water, so that a certain weight (W) must be put into the pan to sink the apparatus to a fixed point marked on the rod (as c). The given body, which must weigh less than W, is placed in the pan, and enought weights (w) added to sink the point c, to the water line It is evident that the weight of the given body is W-w." -Avery 1895

Nicholson Hydrometer

"The Nicholson hydrometer of constant volume is a hollow cylinder carrying at its lower end a basket,…