Mantra 10
    same śucau śarkarāvahnivālukā- vivarjite śabdajalāśrayādibhiḥ / 
    mano'nukūle na tu cakṣupīḍane guhānivātāśrayaṇe prayojayet // 2.10 // 
Let yoga be  practiced within a cave protected from the high wind, or in a place which is  level, pure and free from pebbles, gravel and fire, undisturbed by the noise of  water or of market-booths and which is delightful to the mind and not offensive  to the eye. 
The importance  of physical surroundings is highlighted here. A congenial place and ambience is  always recommended for Yogic Practices in various scriptures. A convenient  location without external disturbances caused by noise, fire, human traffic  etc., and also pleasing to the eye is recommended to help concentration of mind  and still the senses. 
A reference may  be made to the Bhagavad Gita which says: 
yogee yunjeeta satatamaatmaanam rahasi sthitah
    ekaakee yatachittatmaa niraasheeraparigrahah  // 6.10 //
    shuchau deshe pratishthaapya sthiramaasanamaatmanah
    naatyucchritam naatineecham chailaajinakushottaram  // 6.11 //
    tatraikaagram manah kritwaa yatachittendriyakriyah
    upavishyaasane yunjyaadyogamaatmavishuddhaye  // 6.12 //
“A Yogi should always try  constantly to concentrate his mind (on the Supreme Self), remaining in  solitude, living alone with the mind and body controlled, free from desires and  possessions. Having established in a clean spot his firm seat, neither too high  nor too low, made of a cloth, a skin and Kusa grass, one over the other. There,  having made the mind one-pointed, with actions of the mind and sense  controlled, let him, seated on the seat, practice yoga for the purification of  the self”.
The main point  to keep in mind is to concentrate the mind on Brahman in a calm and peaceful  environment.
Mantra 11
nīhāradhūmārkānalānilānāṃ khadyotavidyutsphaṭikāśaśīnām / 
    etāni rūpāṇi puraḥsarāṇi brahmaṇy abhivyaktikarāṇi yoge // 2.11 // 
When yoga is  practiced, the forms which appear first and which gradually manifest Brahman  are those of  snow-flakes, smoke, sun,  wind, fire, fire-flies, lightning, crystal and the moon. 
Certain visions which the seeker experiences as the  forerunners to the revelation of Brahman in the path of Yoga have been  described. They indicate the progress in the Yogic Path. But one should keep in  mind that visions do not occur to all and the crux of the matter is the change  of character of the seeker for better whether visions occur or not. The idea is  that if one has many visions but no transformation in character those visions  are as good as useless. The main thing to observe is whether those visions  enhance one’s God vision or not.
Mantra 12
pṛthvyaptejo'nilakhe samutthite  pañcātmake yogaguṇe pravṛtte /  
    na tasya rogo na jarā na mṛtyuḥ prāptasya yogāgnimayaṃ śarīram // 2.12 // 
When earth,  water fire, air and akasa arise, that is to say, when the five attributes of  the elements, mentioned in the books on yoga, become manifest then the yogi's  body becomes purified by the fire of yoga and he is free from illness, old age  and death. 
In this Mantra and the next the emanation of subtle powers  of the sense organs due to the gross personality becoming subtle by the  practice of Yoga are being described. Each of the subtle elements is endowed  with its unique characteristic like earth with smell, water with taste, fire  with form, air with touch and akasa (space) with sound. Through  concentration the Yogi can experience these attributes. Thus by concentrating  on the tip of the nose he enjoys a heavenly fragrance; by concentrating on the  tip of the tongue; a heavenly flavor; on the middle of the tongue, a heavenly  touch; on the root of the tongue, a heavenly sound. By means of these  perceptions the whole personality becomes subtle and the mind becomes steady,  for it is no longer attracted by outward objects. This is referred to as  attaining siddhi in Patanjali Yoga Sutras. But the seeker should not  become arrogant with attaining these powers as his final goal is realizing  Brahman.
Mantra 13
laghutvam ārogyam alolupatvaṃ varṇaprasādaḥ svarasauṣṭhavaṃ ca / 
    gandhaḥ śubho mūtrapurīṣam alpaṃ yogapravṛttiṃ prathamāṃ vadanti // 2.13 // 
The  precursors of perfection in yoga, they say, are lightness and healthiness of  the body, absence of desire, clear complexion, and pleasantness of voice, sweet  odor and slight excretions. 
The previous  Mantra told us that Pranayama awakens the subtle powers in the seeker. This  Mantra gives the details about the effect of such awakening on the body such as  lightness, clear complexion etc. But it should always be noted that these are  only initial stages and Pranayama should not be considered as the final  objective. It is only a purification process for the final goal of  concentration and self-absorption in Brahman.
VISION OF GOD
Mantra 14
yathaiva bimbaṃ mṛdayopaliptaṃ tejomayaṃ bhrājate tat sudhāntam / 
    tad vātmatattvaṃ prasamīkṣya dehī ekaḥ kṛtārtho bhavate vītaśokaḥ // 2.14 // 
As gold  covered by earth shines bright after it has been purified, so also the yogi,  realizing the truth of Atman, becomes one with the non-dual Atman, attains the  goal and is free from grief.
The seeker’s  attainment of the state of Samadhi is described in this Mantra. A gold plate  covered with dust regains its original state of brightness and shining when the  dust gathered on it is rubbed out. So too, from the state of ignorance when the  impurity of subject-object relationship is removed the real nature of Pure  Consciousness or Atman shines forth and the seeker attains the non-dual  perception of universal unity.  Avidya is  the dirt, Sadhana is Tapas and Pranayama is the means to achieve this goal. The  seeker then becomes free from all sorrows of the world of duality.
SELF-KNOWLEDGE DESTROYS GRIEF
Mantra 15
yad ātmatattvena tu brahmatattvaṃ dīpopameneha yuktaḥ prapaśyet / 
    ajaṃ dhruvaṃ sarvatattvair viśuddhaṃ jñātvā devaṃ mucyate sarvapāśaiḥ // 2.15 // 
And when the  yogi beholds the real nature of Brahman, through the Knowledge of the Self,  radiant as a lamp, then, having known the unborn and immutable Lord, who is  untouched by ignorance and its effects, he is freed from all fetters. 
The question  what happens when the seeker is absolutely purified by knowledge is answered in  this Mantra. The answer is that he simultaneously realizes his identity with  Brahman just like a lamp becomes luminous when it is lit. As the luminosity is  the very nature of the lamp which it regains when it is lighted so also the  seeker identifies himself with Brahman and its power the moment he acquires  Self-Realization. The point to note is that the identity of Sadhaka with  Brahman is not something which is attained but it is their very nature, an  eternal fact, which is cognized only in Samadhi. The realization is that the  seeker was never different from Brahman or the thing that is sought just as the  lamp and its luminosity were never different from each other and that there was  never a Sadhaka really speaking. Thus Shuddha Atma and Shuddha Mind are one and  the same.
IMMANANENCE OF GOD
Mantra 16
eṣa ha devaḥ pradiśo 'nu sarvāḥ pūrvo ha jātaḥ sa u garbhe antaḥ / 
    sa eva jātaḥ sa janiṣyamānaḥ pratyaṅ janās tiṣṭhati sarvatomukhaḥ // 2.16 // 
He indeed,  the Lord, who pervades all regions, was the first to be born and it is He who  dwells in the womb of the universe. It is He, again, who is born as a child and  He will be born in the future, He stands behind all persons and His face is  everywhere.
On attaining  Self-Knowledge the seeker starts looking at the world through a different  looking-glass. Earlier he was feeling ‘I am’, ‘My body’ ‘Your house’ etc., and  now he feels that all relative things of the world as that very Brahman itself.  He sees the gross world of multiplicities as the manifestation of Brahman and  that there is no difference between them - he concludes ‘Verily all this is  Brahman’, “sarvam khalu idam brahma”.   Everything that is perceived in human consciousness is seen as the  manifestation of Brahman. This truth becomes a fact in the Sadhaka’s life. This  is called ‘samyakdarshana’.
CONCLUSION
Mantra 17
yo devo agnau yo apsu yo viśvaṃ bhuvanam āviveśa / 
    ya osadhīṣu yo vanaspatīṣu tasmai devāya namo namaḥ // 2.17 // 
The  Self-luminous Lord, who is fire, who is in water, who has entered into the  whole world, who is in plants, who is in trees - to that Lord let there be  adoration! Yea, let there be adoration! 
So far the  seeker was adoring the Lord  as an  auxiliary aid to Sadhana and now he adores the Lord as an expression of  devotion or bhakti wherein no dualistic salutation is meant but a  salutation in which the person who salutes, the saluted and the salutation all  three are the one Brahman. Such a realized person points out that the same God  who is in the fire, water and who pervades the whole world is in the plants as  well as in big trees, and everywhere. He salutes such a God again and again  indicating that there is nothing other than God anywhere including himself and  his salutations. “Not I, but Thou and Thou alone”. This is Advaita and Bhakti.  The whole Sadhana is a blend of Bhakti and Jnana.
Iti Svetasvataropanishadi  dvitiyo’dhyayah ||
  HERE ENDS THE SECOND CHAPTER OF THE SVETASVATARA  UPANISHAD