The structure of all animal hairs is very complicated, and presents many difficulties, both to the scientific observer and to those who require to manipulate these fibres in the various processes of textile and other manufactures.

As appendages of the skin they are liable, like all the epidermal growths, to great variation in structure, which is seen in its extreme form in the feathers of birds, and in the horns, hoofs, nails, and claws of the higher mammals.

The “twist surfaces,” of which this is a case, stand in the same relation to the helicoid surface as the anchor-ring does to the cylinder. In the helicoid the generating line, at right angles to the axis, rotates about the axis as the point of intersection moves along it. In the twist surfaces the generating line is always at right angles to a fixed circle, and rotates about the tangent to the circle at the point of intersection, as the point of intersection moves round the circle. The species of twist surface is defined by the ratio of the angular motion of the generating line to that of the point of intersection. In the particular case illustrated by the model, the generating line turns through two right angles, while the point of intersection makes one whole revolution; that is, the rate of angular motion of the generating line is one-half of that of the point of intersection.

In August of last year I was in South Uist on an angling expedition, and, while fishing one of the lochs on the island, my attention was drawn to some very remarkable balls that were lying in great numbers at the bottom. I examined a good many of these, and found that they were composed of innumerable algal filaments so intertwined and matted together as to form an outer covering of an almost felt-like consistency, which could, however, be torn open without difficulty. This outer coating varied (speaking very roughly) from about a twentieth to two-twentieths of an inch in thickness, or even more, and the interior of the balls consisted, so far as the naked eye could see, only of mud. The microscope, of course, tells a different story.

The lacquer tree (Rhus vernicifera) is indigenous to Japan; it supplies a valuable timber, and its fruit yields vegetable wax, but it is chiefly cultivated on account of its juice–lacquer (Urushi)–which forms the basis of the famous Japanese varnishes. The juice is obtained by making incisions in the tree, and it is made into a varnish by simply stirring in the sun in order to drive off an excess of moisture. Different colours may be imparted to the varnish by the addition of various metals, oxides, and sulphides; and after it has been applied to an object it must be hardened by exposure to a moist atmosphere at a moderately high temperature.

The Indians, to whom the preparation of these heads is traced, are scattered over a wide tract of country on the eastern side of the Andes. They are known under the general designation Macao, the name of the region they inhabit—a designation which includes the Jivaros, Pastazas, Mendes, Tumbas, and more than twenty other tribes. Early brought into contact with the first Spanish invaders, they suffered much at their hands. Many references to them occur in the history of the Spanish settlers. Their appearance, social habits, and superstitious practices have much prominence given to them in the recent literature of South American travel. At present I limit my remarks mainly to the specimens of “shrunk” or reduced heads now before us. They are from several points of view remarkable, and raise several questions of great ethnological interest, but trustworthy references to them are comparatively few. Indeed, the only sources of information worth mentioning are a communication by Mr William Bollaert, F.R.G.S., to the Ethnological Society of London, 1860, and another, by Sir John Lubbock, to the Anthropological Institute of Great Britain in 1873. The former is entitled “On the Idol Human Head of the Jivaro Indians in Ecuador;” the latter, “Note on the Macas Indians.” In Mr Bollaert's paper special attention is given to a specimen obtained by M. José Felix Barriero, of the Secretariat of the Provincial Government, Quito, and sent by him to Don R. de Silva Ferro, Chilian Consul, London. This specimen was placed in the Ecuador Court of the International Exhibition, 1862. Sir John Lubbock's paper is devoted chiefly to a general description of the Macas Indians.

While collecting materials for a Text-book of the Properties of Matter, the author had occasion to consult the very curious pamphlet by Robert Hooke, entitled Lectures de Potentia Reditutiva, or of Spring (London, 1678). In this work there is a clear statement of the principle of Synchronism, which was applied by Stokes to the explanation of the basis of Spectrum Analysis. There is also a very remarkable statement of the elementary principles of the modern Kinetic Theory of Gases, the first mention of which is usually fixed sixty years later, and ascribed to D. Bernoulli in his Hydrodynamica (Argentorati, 1738).

The first point referred to in this paper is the source of the vapour that condenses to form dew. A few observations of the temperature of the ground near the surface and of the air over it, first raised doubts in the mind of the author as to the correctness of the now generally-received opinion that dew is formed of vapour existing at the time in the air. These observations, made at night, showed the ground at a short distance below the surface to be always hotter than the air over it; and it was thought that so long as this excess is sufficient to keep the temperature of the surface of the ground above the dew-point of the air, it will, if moist, give off vapour; and it will be this rising vapour that will condense on the grass and form dew, and not the vapour that was previously present in the air.

The first question to be determined was whether vapour does, or does not, rise from the ground on dewy nights. One method tried of testing this point was by placing over the grass, in an inverted position, shallow trays made of thin metal and painted. These trays were put over the ground to be tested, after sunset, and examined at night, and also next morning. It was expected that, if vapour was rising from the ground during dewy nights, it would be trapped inside the trays. The result in all the experiments was that the inside was dewed every night, and the grass inside was wetter than that outside. On some nights there was no dew on the outside of the trays, and on all nights the inside deposit was heavier than the outside one.