Given latitude N. 40 deg. 51', declination N. 20 deg. 25', sun 18 deg. below the horizon. To find the time of twilight at that place. In the accompanying diagram, E Q = equinoctial, D D = parallel of declination, Z S N a vertical circle, H O = the horizon, P = North pole, Z = zenith, and S = the sun, 18 deg. below the horizon, H O, measured on a vertical circle. It is seen that we have here given us the three sides of a spherical triangle, viz., the co-latitude 49 deg. 9', the co declination 69 deg. 35', and the zenith distance 108 deg., with which to compute the angle Z P S. This angle is found to be 139 deg. 16' 5.6". Dividing this by 15 we have 9 h. 16 m. 24.4 s., from noon to the beginning or termination of twilight. Now, in the given latitude and declination, the sun's center coincides with the horizon at sunset (allowance being made for refraction), at 7 h. 18 m. 29.3 s. from apparent noon. Then if we subtract 7 h. 18 m. 29.3 s. from 9 h. 16 m. 24.4 s., we shall have 1 h. 57 m. 55.1 s. as the duration of twilight. But the real time of sunset must be computed when the sun has descended about 50' below the horizon, at which point the sun's upper limb coincides with the line, H O, of the horizon. This takes place 7 h. 16 m. 30.8 s. mean time. It is hoped the above will be a sufficient answer to L.N. (See SCIENTIFIC AMERICAN of Dec. 1, 1883, p. 346.) B.W. H. [Illustration] * * * * * ETHNOLOGICAL NOTES. The distinguished anthropologist M. De Quatrefages has recently spoken before the Academy of Sciences in Paris, and we extract from his discourse on "Fossil Man and Savages" some notes reported in the _Journal d'Hygiene_: "It is in Oceanica and above all in Melanesia and in Polynesia where I have looked for examples of savage races. I have scarcely spoken of the Malays except to bring to the surface the features which distinguish them among the ethnic groups which they at times touch, and which in turn frequently mingle with them. I have especially studied the Papuans and Negritos. The Papuans are an exclusively Pelasgic race, that many anthropologists consider as almost confined to New Guinea and the neighboring archipelago. But it becomes more and more manifest that they have had also periods of expansion and of dissemination. "On one side they appear as conquerors in some islands of Micronesia; on the other we have shown--M. Hamy and myself--that to them alone can be assigned the skulls found in Easter Island and in New Zealand. They have hence touched the east and south, the extremities of the maritime world. "The Negritos, scarcely known a few years ago, and to-day confounded with the Papuans by some anthropologists, have spread to the west and northwest.