TEE PROGRESS OF SCIENCE 



617 



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. 



