See biography by A. B. Hawkins (1970).
Among other things, he invented a circular saw, and he was one of the early makers of daguerrotypes. He held several patents for mechanical devices.
He approached the mind-body problem by reasoning that mind was "spiritual matter", observing that man "exists outside himself," and that mind and body, although of two different natures, interact with each other.
From the conclusions of these studies combined with his knowledge of the philosophy and science of the mind, Phineas Quimby developed his theory of mental healing and opened an office in Portland, Maine in 1859.
Quimby claimed that disease is not the cause of illness, but the effect of a conflict existing within the mind; he claimed that all mental and most physical diseases were the result of faulty reasoning. He said "the explanation is the cure."
He treated over 12,000 people in the last 8 years of his life, using his own unique process which he termed "The Quimby System".
He also came to believe that many religious beliefs and opinions were the root cause of a great percentage of all the diseases he treated.
Warren Felt Evans was one of the first individuals who wrote seriously on the teachings of Phineas Quimby. Though he did not specifically establish a movement under these teachings he did open a practice in Salisbury, Massachusetts. Although the most important gift that Evans left to New Thought was his written work, Evans also took the important step of integrating the philosophies of Swedenborg and Quimby.
Here are some references on this point:
‘Quimby’s son and defender said categorically, “The religion which [Mrs. Eddy] teaches certainly is hers, for which I cannot be too thankful; for I should be loath to go down to my grave feeling that my father was in any way connected with ‘Christian Science.’...In [Quimby’s method of] curing the sick, religion played no part. There were no prayers, there was no asking assistance from God or any other divinity. He cured by his wisdom”’ (Dresser, Horatio W., ed. The Quimby Manuscripts. New York: Thomas Y. Crowell Company Publishers, 1921. - p436)
"Christian Science is a religious teaching and only incidentally a healing method. Quimbyism was a healing method and only incidentally a religious teaching. If one examines the religious implications or aspects of Quimby’s thought, it is clear that in these terms it has nothing whatever in common with Christian Science” (Gottschalk, Stephen. The Emergence of Christian Science in American Religious Life. Berkeley: University of California Press, 1973 - p130)"
“[Julius] Dresser sees the healing power [of Quimby] as a kind of clairvoyance, an ability to enter into the sick person’s mind and read his or her thoughts; Dresser makes no suggestion that this type of healing involves tapping into a divine strength, as Mrs. Eddy would later claim for her Christian Science” (Gill, Gillian. Mary Baker Eddy. Cambridge, Mass.: Perseus Books, 1998 - p159).
“That which connected her [Eddy] with Quimby was her conviction that all disease in the last analysis has its roots in the mind, and that healing therefore must be effected through mental influence. But it was her earnest Puritan faith in God that separated her from Quimby from the beginning.” (Karl Holl, German Historian)
A good composite of both Quimby, and the incompatibility of his ideas and practice with those of Eddy, can be found in these sources: Taves, Ann, Fits, Trances, & Visions: Experiencing Religion and Explaining Experience from Wesley to James. Princeton University Press 1999 (pp 212-218); Peel, Robert. Mary Baker Eddy: The Years of Discovery. Boston: Holt, Rinehart and Winston, 1966 (chapter, “Portland 1862”); Gill, Gillian. Mary Baker Eddy. Cambridge, Mass.: Perseus Books, 1998 (pp 131-146 & 230-233).