But the vibration which takes place in the surface of the envelope of the outer balloon is _across_ this line of propagation, because as the wave proceeds from _A_ to _B_, the elastic envelope expands and stretches always _across_ the line of propagation--that is, it stretches up and down, left and right, as it is expanded outwards, so that the vibration or oscillation of the particles always takes place in the surface of the elastic envelope across the line of propagation. Let us therefore apply the result of this simple experiment to our solar system and the Aether, and see if it can be made to explain the transverse vibration of light. Let _A_ represent the sun (Fig. 7) and _B_ an aetherial elastic envelope surrounding the sun. In this case we dispense with the bulb _C_, as the sun possesses within itself the power to generate heat, and so to produce the required expansion of the elastic aetherial envelopes _B_, _G_, _H_, etc. [Illustration: Fig: 7.] Instead, however, of having air particles between _A_ and _B_, we will put in their place our aetherial atoms which we have conceived according to Art. 44. These surround the sun, represented by _A_, forming elastic spherical shells or envelopes. As the sun radiates its heat into space, it urges the aetherial atoms against each other, with the result that they transmit the energy from atom to atom, or particle to particle, till they come to the elastic aetherial envelopes of _H_, _G_, _B_. The effect on _B_, or on any other aetherial envelope, is to expand it outwardly, and thus set the atoms of which it is composed into vibration. The wave, which is now an aetherial wave travelling with a velocity of 186,000 miles per second, may be represented by the line _D_ _E_. But while it is travelling from _D_ to _E_ the same energy is being radiated out in all directions, so that a wave reaches the whole surface of the elastic envelope _B_ at the same time, with the result that the whole of the shell or envelope is set in vibration as it expands outwardly. Thus the vibration is always in the wave front, and the wave front is always coincident with the surface of one of these envelopes, and as these aetherial envelopes are themselves formed by aetherial atoms, the wave is spread outwardly from any central point in a spherical form as proved by experiment. Not only, therefore, is the vibration in the wave front, but it is always transverse to the line of propagation, for the simple reason that the surface of the spherical shell or envelope is always at right angles to the radius vector or straight line which joins any centre to the surface of a spherical envelope.