The value of the coefficient of conductivity for ice is an important desideratum in several branches of physics; and it derives additional importance from an application, explained in the second part of this communication, to the determination of the thermal conductivity of different substances in absolute measure. The brilliant researches of Neumann, and some ingenious experiments by M. Lucien De La Rive, afford us at present the only two determinations that we possess of this important quantity. The value found by Neumann is 0·114, while De La Rive makes it 0·138. The discrepancy justifies the publication of experiments on a some-what large scale, which gives us a close approximation to the truth.