Page:Popular Science Monthly Volume 85.djvu/621

Rh shown signs of inefficiency. For example, it seems unable to account for the so-called photo-electric phenomena. Incapacity has been still more obvious in connection with the properties of X-rays. At one time it seemed, at least to some, easier to deny the identity of light-and X-rays than to force the orthodox theory to yield an explanation of X-ray effects. When therefore the identity is established by the new experiment, a very interesting position results. The orthodox theory is to be supplemented in some way not yet clear. It will then be, surely, far more effective than it ever has been before. From our new point of view our difficulties are more clearly defined, but, at the same time, we shall probably receive new help to their solution.

In the second place a method of analyzing X-rays has been evolved from the original experiment. The wave lengths of X-rays can now be measured exactly, and other characteristics of X-rays can be expressed in terms of these. Remarkable relations have already been found to exist, for instance, between the wave lengths of the X-rays emitted by various atoms under proper stimulus and the positions of those atoms in the table of Mendelejeff. Much light is thereby thrown upon the meaning of the table, and a limit is set to the number of its vacant places, that is to say of elements not yet discovered.

Again, the new experiments provide a means of investigating the structure of crystals. We are able to determine the arrangement of the atoms in a crystal and to measure the distance from atom to atom. The science of crystallography can be built on a firmer basis than before, for it can now take account of the internal structure of the crystals whereas it has hitherto relied on observations of the external form.

Finally, the motions of the atoms about their average positions are made manifest. Little experimental work has yet been done in this direction, but it does not seem unlikely that we shall presently measure with exactness the extent of the atomic movements which contribute to the heat content of a body.

Professor Bragg's lectures were devoted to an attempt to explain more fully the statements outlined above. In the first lecture the general question was considered. Laue's experiment was described and interpreted and its meaning discussed. The subject of the second was W. L. Bragg's restatement of Laue's theory, together with its important consequence, viz., the X-ray spectrometer and its powers. The third was devoted to the consideration of crystal structure in the light of the new discovery, and the fourth to X-ray spectra, the relation of X-ray properties to wave length, and the thermal movement of the atoms in the crystal.

connection with the rearranging of the scenic effect of one of the Roosevelt animal groups in the National Museum, actual African plants and grasses, are to be filled with plaster and preserved in their natural state to give the animal specimens local color. In the art of modern taxidermy the old system of simply "stuffing" the skins of animals has been done away with, and at standard method of accurate life-size modeling established. Over a carefully made plaster cast of this model the skin is stretched, glued and sewed, so that it is difficult to see how it was accomplished; for the moment it is easy to believe that the animal itself has been preserved intact in some marvelous manner.

For many years past the National Museum has been employing natural scenery—real grass, foliage and soil—in its biologic and ethnographic groups, much as in theatrical effects, to create a natural atmosphere. Now-a-days, museums do not simply mount individual animals on a platform and place them in a case. They are mounted in natural attitudes, and ground work, suitable to both the environment and the posture of the figures, is prepared.