De Broglie now found that the velocity of the material point was in fact the group velocity of the matter-wave. De Broglie's theory of matter-waves subsequently recieved experimental confirmation. If a relatively slowly travelling electron meets a crystal surface, diffraction and reflection phenomena appear in the same way as if an incident beam of waves were concerned. As a result of this theory on is forced to the conclusion to conceive of matter as not being durable, or that it can have definite extension in space. The waves, which form the matter, travel, infact, with different velocity and must, therefore, sooner or later separate.
Matter changes form and extent in space.
The picture which has been created, of matter being composed of unchangeable particles, must be modified. One of the physical phenomena whose correct explanation has proved most difficult, is the apperance of the spectra of countless lines and bands which are obtained if light is split up by optical instruments when produced by atoms and molecules as a result of their vibrations. It has been known for a long time that each such line corresponds to light of a certain frequency, which varies according to where the line appears in the various parts of the colour spectrum. A correct explanation of the intensities of all these lines and their positions in the spectrum is of fundamental significance since it gives an insight into the structure of the atoms and molecules and the relationships within them. It was Bohr who, in 1913, expressed the idea that Planck's constant should be taken as the determining factor for movements within the atom, as well as for the emission and absorption of light waves.