I am a volunteer for Project Gutenberg, and most of the texts listed below will also be available at that site. 

Aesthetics

Lee, Vernon.  The beautiful (1913).  Read Online/Download 

Lee, Vernon.  Laurus nobilis; chapters on art and life (1909).  Read Online/Download 

Noyes, Carleton.  The enjoyment of art (1903).  Read Online/Download  

Noyes, Carleton.  The gate of appreciation (1907).  Read Online/Download  

Santayana, George.  The sense of beauty; being the outlines of aesthetic theory (1896).  Read Online/Download 

Souriau, Paul.  La rèverie esthétique; essay sur la psychologie du poète (1906).  Read Online/Download

Taylor, Thomas, trans.  An essay on the beautiful (from the Greek of Plotinus) (1917).  Read Online/Download 

Affirmations

Coué, Émile.  Self mastery through conscious autosuggestion (1922).  Read Online/Download 

Leland, Charles Godfrey.  The mystic will (1907).  Review  •   Read Online/Download

Divination

"Clara".  Cupology (1904).  Review  •   Read Online/Download

"A Highland Seer".  Tea-cup reading (1921.)  Review  •   Read Online/Download

Sepharial.  How to read the crystal, or crystal and seer (1922).  Review  •   Read Online/Download

Sepharial.  Second sight (1912).  Review  •   Read Online/Download

Stevenson, E. Irenaeus.  The square of sevens (1896).  Review  •   Read Online/Download

Fin-de-Siècle

Custance, Olive (Lady Alfred Douglas).  The inn of dreams (1911).  Read Online/Download

Ficke, Arthur Davison and Witter Bynner.  Spectra (1912).  Review  •   Read Online/Download

Gautier, Théophile.  Enamels and cameos (1903).  Read Online/Download

Gray, John.  Silverpoints (1893).  Read Online/Download

Merrill, Stuart.  Petits poèmes d'automne (1895).  Review  •   Read Online/Download

Scheffauer, Herman.  The masque of the elements (1912).  Read Online/Download

Symons, Arthur.  Silhouettes (1896).  Read Online/Download

Taylor, Rachel Annand.  The hours of Fiammetta.  A sonnet sequence (1910).  Read Online/Download

Ruth Hart

Hart, Ruth. Thunderbroom (2009).  Read Online/Download.  (Also available as PDF).

Herbalism

Fernie, William T.  Herbal simples approved for modern uses of cure (1897).  Review  •   Read Online/Download  

Philosophy

Epictetus.  The enchiridion (1750).  Read Online/Download

Epicurus.  Principle doctrines (1925).  Read Online/Download

John Cowper Powys

Powys, John Cowper.  The complex vision (1920).  Review  •   Read Online/Download

Powys, John Cowper.  The secret of self development (1926).  Read Online/Download  

Powys, John Cowper.  Suspended judgments: essays on books and sensations (1916).  Read Online/Download 

Powys, John Cowper.  Visions and revisions: a book of literary devotions (1915).  Read Online/Download 

Spirituality

Emerson, Ralph Waldo.  Nature (1849).  Read Online/Download

Hung, Tzu-ch'eng.  Musings of a Chinese vegetarian (1926).  Review  •   Read Online/Download

Mercer, J. Edward.  Nature mysticism (1913).  Review  •   Read Online/Download

Santi-deva.  The path of light (1909).  Read Online/Download

Shastri, M.P.M.R., ed.  The Vijnana Bhairava scripture (1918).  Review  •   Read Online/Download (pdf)

Staveley, Lilian.  The golden fountain (1919).  Read Online/Download

Staveley, Lilian.  The prodigal returns (1921).  Read Online/Download

Staveley, Lilian.  The romance of the soul (1920).  Read Online/Download

Underhill, Evelyn.  Practical mysticism (1915).  Review  •   Read Online/Download

Younghusband, Sir Francis.  The heart of nature (1922).  Read Online/Download

Tea

Gray, Arthur.  The little tea book (1903).  Review  •   Read Online/Download

Yanagi, Soetsu.  The way of tea (1953).  Review  •   Read Online/Download