As a child, Dalton longed for a formal education, but his family was very poor. It was clear that he would need to help out with the family finances from a young age.
After attending a Quaker school in his village in Cumberland, when Dalton was just 12 years old he started teaching there. When he was 14, he spent a year working as a farmhand, but decided to return to teaching—this time as an assistant at a Quaker boarding school in Kendal. Within four years, the shy young man was made principal of the school. He remained there until 1793, at which time he became a math and philosophy tutor at the New College in Manchester.
While at New College, Dalton joined the Manchester Literary and Philosophical Society. Membership granted Dalton access to laboratory facilities. For one of his first research projects, Dalton pursued his avid interest in meteorology. He started keeping daily logs of the weather, paying special attention to details such as wind velocity and barometric pressure—a habit Dalton would continue all of his life. His research findings on atmospheric pressure were published in his first book, Meteorological Findings, the year he arrived in Manchester.
During his early career as a scientist, Dalton also researched color blindness—a topic with which he was familiar through firsthand experience. Since the condition had affected both him and his brother since birth, Dalton theorized that it must be hereditary. He proved his theory to be true when genetic analysis of his own eye tissue revealed that he was missing the photoreceptor for perceiving the color green. As a result of his contributions to the understanding of red-green color blindness, the condition is still often referred to as "Daltonism."