M. AMAGAT (Compt. rend.1 , lxxxix. p. 437, corrected Beiblätter , iv. p. 19) has submitted hydrogen, oxygen, nitrogen, air, carbon monoxide, methane, and ethylene at temperatures from 18° to 22° to pressures ranging between 28 and 431 atmospheres, and finds that, except for hydrogen, the product p v first diminishes and then increases as p increases, the most marked case being that of ethylene, for which the values of p v at 31.58, 84.16, 398.71 atmospheres are proportional to 2.29, 1, 3.13 respectively. Dr. van der Waals deduced this general peculiarity theoretically in 1873, and showed that its markedness is the greater, the less the temperature of compression exceeds the critical temperature: concluding, therefore, that for ethylene the critical temperature is not far below 18°, as M. Amagat has also surmised, he has recently (Meded. der k. Akad. van Wetenschappen in Amsterdam, Mei 1880)2 determined it directly by a Cailletet compression-apparatus, finding it to be 9°.2, and the critical pressure 58 atmospheres.