Paramhansa Yogananda wrote several mail-order courses. One of them he called ADVANCED SUPER COSMIC SCIENCE COURSE (1934). I've shared below from:
Lesson 1 - Healing by Spiritual Affirmation and by Astral Food
I've excerpted the segment on astral food as follows:
Food in the future -- Energy.
The future food of the world will all come by
receiving different rays from Cosmic Energy, Cosmic Rays, electrons, atoms, and
air, drawn through different openings of the body. [Yogananda's guru, Swami Sri Yukteswar revealed that our planet is in an upward arc of increasing awareness based on certain planetary and astronomical phenomenon. He predicted that our current age, called Dwapara (dwa=second), would see rapid advances of knowledge as to the existence and use of subtle energy and atomic forces or rays.]
From Cosmic Energy.
1. If one constantly keeps his mind concentrated on
the point between the eyebrows (at the Christ Center) and sees there the
Spiritual Eye and commands it to recharge the body with strength, it will do
so. By doing this, people would cease growing old. [Comment: the "spiritual eye" referred to here is a specific image that can be seen by anyone regardless of belief or religion. Most readers of this blog will not require a description of the three concentric circles of gold, blue and a white, five-pointed star. More importantly and richly rewarding is the effort to maintain an awareness of the point between the eyebrows during waking hours, including meditation. By so doing, one's intuitive awareness both in general but also of subtle energy steadily increases. Practicing recharging the body at will as described above comes more easily when our awareness of this point in the body becomes stronger.]
2. Drawing energy from the cerebrum and medulla by
connecting the tip of the big tongue with the little tongue (uvula). [Comment: this is a preliminary stage of the advanced and powerful technique known as kechari mudra. See Swami Kriyananda's classic text, "Art and Science of Raja Yoga," Step 13, Yoga Postures, for an explanation.]
From the Sun.
3. Energy may be drawn from the sun by covering the
whole body with a piece of thick blue silk or a blanket and keeping the medulla
exposed with the sun shining there, on the back of the head. Concentrate on the
back of the head and feel it getting warmer and warmer. Feel the energy being
stored in the brain and distributed through the body. [Yogananda elsewhere describes the valuable technique known as "Sun-Gazing." In the first or final minutes of sunrise or sunset it consists of gazing into the sun in a very specific manner at a time when it is safe to do so.]
4. Take a sunbath and concentrate deeply upon the
sun-bathed surface of the body, and drink the sunshine in through every pore of
the body. Concentration on the sun rays gives one hundred times greater results
than taking a sunbath absentmindedly. [Comment: in Yogananda's day concern for cancer from sun-bathing was more or less unknown. In some of his other lessons, he was careful to suggest as few as ten minutes exposure. Each person should determine what is best for themself.]
From Electrons.
In order to receive electronic energy from the
ether, expel the breath, remain calm while sitting in the erect posture, and
feel the electronic energy surrounding your body and entering through your body
cells, or receive energy through your fingers while your hands are lifted over
your head.
From Oxygen.
Sit upright on a chair. Close your eyes. Expel the
breath quickly, but start inhaling very slowly through nostrils, thinking that
the air is filling your brain, lungs, heart, spine, stomach, abdomen, thighs,
legs, arms, and so forth. You can also inhale quickly and fill the whole body
with the atomic power in the oxygen. [In his now-famous "Energization Exercises," Yogananda combined a quick "double" inhalation (short-long) with tensing the entire body, vibrating the entire body, then exhale through the mouth (and nose) with a double exhalation. "Tense with will; relax and feel" he instructed.]
[Below is an affirmation which Yogananda gave as part of this lesson]
"I am Thy son; I am wise.
Thou art happy; I am Thy child, therefore I am a happy child.
Father, Thou hast everthing. I am Thy child; I have everything.
Thou art ever-well; I am well, I am well.
We are Thy children; I wish all to be happy.
Thou art power; I am power."
I hope you will profit from this "food for thought" by Paramhansa Yogananda!
Swami Hrimananda