Question: To whom did Van Gogh write, "I should like to paint portraits which appear after a century to people living then as apparitons."
About the article "Vincent van Gogh", section "Portraits".

Candidate passages:
Van Gogh, known for his landscapes, seemed to find painting portraits his greatest ambition.
To his sister he wrote, "I should like to paint portraits which appear after a century to people living then as apparitions.
By which I mean that I do not endeavor to achieve this through photographic resemblance, but my means of our impassioned emotions -- that is to say using our knowledge and our modern taste for color as a means of arriving at the expression and the intensification of the character.
"While Van Gogh had few opportunities to make portraits, he completed at least three at Saint-Rémy. 
Van Gogh, known for his landscapes, seemed to find painting portraits his greatest ambition.
He said of portrait studies, "the only thing in painting that excites me to the depths of my soul, and which makes me feel the infinite more than anything else."
To his sister he wrote, "I should like to paint portraits which appear after a century to people living then as apparitions.
By which I mean that I do not endeavor to achieve this through photographic resemblance, but my means of our impassioned emotions -- that is to say using our knowledge and our modern taste for color as a means of arriving at the expression and the intensification of the character.
"As much as Van Gogh liked to paint portraits of people, there were few opportunities for him to pay or arrange for models for his work which may have been another factor in his desire to make a portrait of his mother. 
Van Gogh, known for his landscapes, seemed to find painting portraits his greatest ambition.
He said of portrait studies, "the only thing in painting that excites me to the depths of my soul, and which makes me feel the infinite more than anything else.
"To his sister he wrote, "I should like to paint portraits which appear after a century to people living then as apparitions.
By which I mean that I do not endeavor to achieve this through photographic resemblance, but my means of our impassioned emotions -- that is to say using our knowledge and our modern taste for color as a means of arriving at the expression and the intensification of the character."
Although Van Gogh is best known for his landscapes, he seemed to find painting portraits his greatest ambition.
He said of portrait studies, "The only thing in painting that excites me to the depths of my soul, and which makes me feel the infinite more than anything else.
"To his sister he wrote, "I should like to paint portraits which appear after a century to people living then as apparitions.
By which I mean that I do not endeavor to achieve this through photographic resemblance, but my means of our impassioned emotions – that is to say using our knowledge and our modern taste for color as a means of arriving at the expression and the intensification of the character.
"Of painting portraits, Van Gogh wrote: "in a picture I want to say something comforting as music is comforting.
I want to paint men and women with that something of the eternal which the halo used to symbolize, and which we seek to communicate by the actual radiance and vibration of our coloring."
After leaving the south of France, Van Gogh's brother, Theo and artist Camille Pissarro developed a plan for Van Gogh to go to Auvers-sur-Oise with a letter of introduction for Dr. Paul Gachet, a homeopathic physician and art patron who lived in Auvers.
Van Gogh had a room at the inn Auberge Ravoux in Auvers and was under the care and supervision of Dr. Gachet with whom he grew to have a close relationship, "something like another brother.
"For a time, Van Gogh seemed to improve.
He began to paint at such a steady pace, there was barely space in his room for all the finished paintings.
From May until his death on July 29, Van Gogh made about 70 paintings, more than one a day, and many drawings.." Van Gogh painted buildings around the town of Auvers, such as The Church at Auvers, portraits, and the nearby fields.