He spoke fluent Persian and is the author of the book Tashrih al-aqvam(an account of origins and occupations of some of the sects, castes, and tribes of India). It  was completed in 1825 and is part of the collection of the British Library.

Skinner translated into Persian the summary of the Vedas and Shastras with a survey survey of both Hindu and Muslim occupational groups and religious mendicants in the Delhi region.

The book also gives details of   Hindu, Jain, and Sikh religious faqeers (mendicants) such as yogis and sanyasis as well as the Muslim Afghans of Kasur, qawwals, and fakirs.

The text was illustrated by a number of Delhi artists commissioned by Skinner for  the album, the chief of them being Ghulam Ali Khan. The watercolor paintings all seem to have been made from live subjects by the painter who accompanied Skinner on his travels.

Some of them are given here

A Khatri

A Qawwal

Khati or Tarkhan, carpenter caste of the Panjab

The Badhik, (butcher)or sometimes pronounced Badhak are a Hindu caste found in the state of Uttar Pradesh, India

Kamdangar, a bowmaker

Dhundiya, a member of the strict Sthanakavasi sect of Jains. Wearing a mouthcloth to protect microscopic life from harm, he carries a brush to clear insects from his path

A portrait of Bhajan Das Bairagi, a member of the Vaisnava order of ascetics, usually followers of Ramananda

Qusuri or ‘Kusuri, an Afghan of Kasur

An astrologer with his divination board.

Kahar, the carrier or bearer class of the eastern Panjab.

Bavari, an itinerant predatory tribe, represented by a bird-snare

Banjara an itinerant trader, often a grain merchant. Man with oxen carrying sacks

A Harlot

A Barber

A dhobi

A screenmaker-dumna

A Saiva mendicant

A leather bottle maker

Luniya -salt diggers

Mallah- boatmen

Tanner

Gandhi’, a caste of perfumers or druggists, from ‘Tashrih al-aqvam’, 1825 (w/c on paper)

A Mewati warrior

Chipi (or chimba), a cloth printer – Tashrih al-aqvam (1825)
#TashrihAlAqvam – categorisation of castes &occupations

Grain roaster

Bavari, an itinerant predatory tribe, represented by a bird-snarer.

Sadhu – a naked ascetic. This particular one is associated with the ‘Vairagis’ and is armed with a spear, gun and talwar.

A water-seller. Saqqa, a Muslim caste of water-carriers.
Nat – gypsy acrobat

A cotton-dresser. Dhuniya or Pamjara, synonyms for the caste of cotton-dressers, represented by a masked man using a bow to prepare raw cotton

A professional thief

Female conjuror/Bhanmati

Teli

Sabzi farosh /Vegetable seller

Rangrez/dyer

A singer or bard. Bandijan or kalavant, a singer or bard from the Bhat caste.

Kalāl, a caste of distillers and tavern keepers

(Images from Asia society site)