Isaac Newton's letter, titled Letter to True Disciples of Hermes Containing the Six Principal Keys of Secret Philosophy (Epistola ad veros Hermetis discipulos continens claves sex principales Philosophiae secretae)¹ is mostly about the alchemical process. Here are three excerpts that will be explained.
The difficulty of the alchemical work
"I write solely for you, the wise disciples of Hermes and true children of the art, [and] my unique goal is to serve you as a Guide on this difficult journey.
I sincerely testify to you that our art's practice is the most difficult of all things in the whole world, not in relation to its operations, but due to the difficulties of understanding clearly in the writings of the Philosophers. For on one side it is referred to as the "children's play," while on the other, it requires those who, through their labor and study, seek the truth, to have a deep understanding of the principles and operations of nature, especially in the mineral and metallic realms."
Newton certainly knew that alchemy was about the development of consciousness and not the production of a red precious stone. In the quote, he stated the first problem alchemists were confronted to: the difficulty to decipher the symbolic meaning in the writings of the Philosophers.
Alchemy has an exoteric or exterior meaning and an esoteric or hidden one. Most scholars stop at the exoteric interpretation. They think alchemy was the precursor to chemistry and believe that the philosophers were doing chemical experiments. Even C. G. Jung, in his psychological understanding of the alchemical process, thought the the artifex (artisan) was projecting his unconscious on his chemical experiences.
The esoteric or hidden meaning has a lot more sense when we decipher the symbols correctly. Alchemists were deeply interested by the mystical experiences that were produced by the development of their consciousness. Jung's favorite alchemist Gerard Dorn wrote that there are three successive mystical experiences or conjunction of opposites which he named unio mentalis, lapis philosophorum and rotundum. Other mystics also have stated that there are three experiences in the Christian process.
Each alchemist had his own method and terminology to teach the access to those mystical experiences. This is the reason that brought Newton to the statement that the understanding of each alchemist was the most difficult thing to realize. The esoteric meaning of alchemy is always reached with a second degree reading of the alchemists, a technique that asks for a clear understanding of the goal of alchemy.
The prima materia or first matter
"The main point is to find the true material that is the subject of our work. For this, one must penetrate the thousand obscure words in which it is concealed. One must distinguish by its proper name among the hundred thousand extraordinary names by which the Philosophers have variously named it. One must comprehend all its properties and judge all the degrees of perfection that the art can communicate to it. One must know the secret fire of the Wise, which is the only agent that can reveal, sublime, purify, and arrange the material so that it can be reduced to water.
One must penetrate to the source and divine origin of the heavenly water, which works the solution, animation, and purification of the Stone. One must understand the conversion of our metallic water into an unburnable oil through the total dissolution of the body from which it originated. And for this effect, one must perform the conversion of the elements, the separation, and the reunion of the three principles. One must understand how the white mercury should be made..."
Alchemy is based on the four elements of Antiquity. If matter is composed of four elements Air, Fire, Water and Earth, the soul and consciousness has also four directions and are represented with the same symbols. Jung's four cognitive functions directly derive from the four elements. These correspondences are generally admitted:
Earth = sensation
Air = intuition
Water = feeling
Fire = thinking
Humans develop only two cognitive functions and the other two stay in the unconscious. In order to identify which function is where, alchemists used the three principles Sulphur, Mercury and Salt. They would correspond in Jung's system to the auxiliary, tertiary and inferior functions.
The prima materia of achemy is therefore consciousness. The process is to lower the use of a function, beginning with the auxiliary function or Sulfur to make the opposite rise from the unconscious. When both functions have an equal developement, a symbol of conjuntion of opposites apprears in consciousness. Accordingly, Newton wrote:
"And the yellow mercury. It is necessary to fix this mercury and nourish it with its own blood so that it may be transformed into the fixed sulfur of the Philosophers. Behold the fundamental points of our art. The remaining work is sufficiently clearly described in the books of the Philosophers, so it does not require further explanation."
Three Conjunction of Opposites
"Just as there are three Kingdoms in nature, so there are also three medicines in our art, which perform three different operations in practice and which are merely three different degrees that elevate our elixir to its ultimate perfection. These significant operations of the three works are reserved under the key of the arcana by all the Philosophers, so that the sacred mysteries of our divine philosophy are not revealed to the profane. But to you who are the children of science and who can understand the words of the wise, the doors will be opened, and you will have the keys to the precious treasures of nature and art if you apply your mind to understanding what I intend to tell you in terms as intelligible as necessary for those who are predestined, as you are, to the knowledge of these sublime mysteries."
We have already said that there are three conjunction of opposites during the alchemical process. Newton was aware of that fact. The first symbol appears after the developement of the third cognitive function. The second one after the developement of the inferior function. And the final one at the end of the process when consciousness is fully operational. This state is also called the quintessence.
C. G. Jung affirmed that alchemy was an adyton protected by the desidaimonia. In english, that means that alchemy is a secret protected by the wrath of the gods. In the quote above, Newton used the word arcana which has approximately the same meaning. Because alchemy intended to produce mystical experiences in a secular setting, it was imperative for the authors of the grimoires to protect themselves from the Church and the Inquisition. The secret surrounding the processes was absolutely imperative.
¹Keynes MS. 23, King's College Library