Page:Popular Science Monthly Volume 85.djvu/621
TEE PROGRESS OF SCIENCE
��shown signs of inefficiency. For ex- ample, 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 ex- periment, a very interesting position re- sults. 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 diffi- culties are more clearly defined, but, at the same time, we shall probably re- ceive new help to their solution.
In the second place a method of analyzing X-rays has been evolved from tne original experiment. The wave lengths of X-rays can now be meas- ured exactly, and other characteristics of X-rays can be expressed in terms of these. Remarkable relations have al- ready 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 crys- tal and to measure the distance from atom to atom. The science of crystal- lography can be built on a firmer basis than before, for it can now take ac- count 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 exact- ness the extent of the atomic move-
VOL. LXXXV. — 41.
��ments which contribute to the heat con- tent of a body.
Professor Bragg 's lectures were de- voted 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 im- portant 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 proper- ties to wave length, and the thermal movement of the atoms in the crystal.
NATURAL SCENERY FOR MUSEUM EXHIBITS
In connection with the rearranging of the scenic effect of one of the Roose- velt animal groups in the National Mu- seum, actual African plants and grasses, are to be filled with plaster and pre- served in their natural state to give the- animal specimens local color. In the- art of modern taxidermy the old systenti of simply "stuffing" the skins of ani- mals 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 accom- plished; 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 individ- ual 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.