The restraint of rising impressions brings about an undisturbed flow of tranquillity.

Verse 3.9

व्युत्थाननिरोधसंस्कारयोः अभिभवप्रादुर्भावौ निरोधक्षण चित्तान्वयो निरोधपरिणामः ॥९॥

vyutthāna-nirodha-saṁskārayoḥ abhibhava-prādurbhāvau nirodhakṣaṇa cittānvayo nirodha-pariṇāmaḥ ॥9॥

Study of the silent moments between rising and restraining subliminal impressions is the transformation of consciousness towards restraint

Verse 3.10

तस्य प्रशान्तवाहिता संस्कारत् ॥१०॥

tasya praśānta-vāhitā saṁskārat ॥10॥

The restraint of rising impressions brings about an undisturbed flow of

tranquillity.

That is to say, in this first state of Samadhi, the modifications

of the mind have been controlled, but not perfectly, because if they were, there would be no modifications. 

If there is a modification which impels the mind to rush out through the senses, and the Yogi tries to control it, that very control itself will be a modification. One wave will be checked by another wave, so it will not be real Samadhi, when all the waves have subsided, as control itself will be a wave. Yet this lower Samadhi is very much nearer to the higher Samadhi than when the mind comes bubbling out.

The flow of this continuous control of the mind becomes steady when practices day after day and the mind obtains the faculty of constant concentration.

PATANJALI YOGA SUTRAS