To the writer it seems that the Particle of Substance finds within its Mind-principle (for you know we have seen that all Substance had something akin to Life and Mind) a constant craving, imbedded in its very nature, which causes it to seek Satisfaction. This craving for Satisfaction results in Unrest, and seeks a solution along two lines. These two lines are indicated by two entirely different Desires that it finds within itself--the first being a Desire or Inclination to seek the companionship of some other Particle--the second being a Desire or Inclination to be Free of Attachment or Entanglement. The Desire for Attachment arises from the force of the Law of Attraction that exists between each Particle of Substance. The Desire for Non-attachment arises from some inward inclination for Freedom. These two Desires or Inclinations may be called the Desire for Impression and the Desire for Expression. The Desire for Impression (or pressing in) manifests along lines of action tending toward Attachment, Moreness, Companionship, Combination. The Desire for Expression (or pressing out) manifests along the lines of action tending toward Individuality, Freedom, Independence, Unattachment, etc. And both are strong cravings--and both tend to produce Unrest, which results in Motion. The "pull" of the Desire of Impression exists always, and is always modified and counteracted by the "push" of the Desire for Expression. And, resulting from the play of these two Desires, or Forces, result Activity, Motion and Change. Like the two conflicting angels in the Persian mythology--Ahriman and Ormuzd--these two Desires wrestle with each other in the theatre of the Universe--constant Motion and Change being the results. And, if the writer may be pardoned for dropping into Mysticism for the moment, may it not be that these conflicting Desires for Separateness and Unity, respectively, are but different forms of the Desire for Satisfaction through Oneness. Impression seeks Oneness by combination with other separated Particles, _but finds it not_. Expression seeks Oneness by drawing apart and endeavoring to realize it in that way, _but finds it not_. But both are but different aspects of the same Desire for Satisfaction, and only when the Mind recognizes Oneness in Diversity does Satisfaction come. And thus the lesson of the Particle becomes the Lesson of the Man. These conflicting Desires of Inclinations of the Particles--the one urging it along the lines of Attraction--the other along the lines of Separation--produce the Dance of the Atoms--the Motion of the Particles.