Didn't mean to come across as you sounding accusatory, just meant that Tohei had the "stuff" that Aikido is made of.
Describing ki is a lot like trying to describe water without using the word "wet". The whole purpose of Aikido is to reach a balance of energy, technique, and spiritual blending with both your attacker and his attack. Ai (same) ki (energy) do (way) is the dictionary definition, but like anything done by the esoteric thinkers, they leave out more than they put in the definition.
Breath and timing are the two most physical elements of the techniques that have a difficulty factor of 10 on a scale of 1 to 10 where 10 is most difficult. When you combine it with posture, mental clarity, and meeting the attack before it "matures", takes the difficulty factor off the charts.
Ki has several conditions... if you are extending ki, you are extremely strong and your body is totally in balance. If you are "sucking in" ki, you are almost totally at the mercy of the attack, and if you are "meeting ki" you are not blending with the attack, so it's not aikido.
I don't know if there IS a physical description of ki that is accurate, because it is like breath and timing... always changing and always in a differing condition in your practice. I've learned physical tricks to use that make what I do look like magic, but it's really just blending with the attack and then extending a little ki, but it crushes the attacker like bug.
Mind you that I use jujitsu as much or more than I use aikido in my teaching, because the art of Aikido is a pared-down version of several types and styles of jujitsu. It's main derivative is from Daito Ryu Jujitsu, but its technique is studied as a jitsu and not a "do" in that art. If that's confusing, it's because you need to understand the differences between "jitsu" and "do". Jitsus are "methods" and "do" is "way or path". One of the other tricks the esoteric thinkers play on westerners is to have multiple meanings for their words. Where "ju" is always interpreted as "soft or pliable", it also means "easy", so "jujitsu" translates into "easy method" rather than "soft method". Judo is another tricky moniker for an art, because if you try to interpret it as "easy path or way", it is certainly not that... it is a complicated and very scholarly dissection and reassembly of numerous jujitsu styles that Professor Kano used to design a competitive sport. At the time he was organizing it, many of the techniques left people permanently damaged from the practices they used. He took those elements out of his Judo to allow people to practice without being crippled for life. He did not create the actual moniker "Judo", for there were numerous "judos" out there being practiced, but he organized the techniques and dissected the techniques to make them safe for the general public to practice. His "judo" is what the public sees today.
One of my favorite ways of describing techniques in Aikido and Jujitsu, is to tell someone that "there's more than one way to skin a cat, but there's no way to make the cat like it". What that means is that there are numerous ways to accomplish the same thing... a throw for instance, can be accomplished by using "leading and ki application" like Aikido, "leverage" as in Judo, or simply blocking and driving through the opponent to make them lose their balance. In all three, you can use (or not)ki to accomplish the task, but you still end up with the same result. Some of the methods are more difficult than others, so you have to study them to figure out if you want to become a "leverage" expert, an "Aikido" expert, or just someone that has fighting abilities and uses a different arrow from their quiver depending upon the attack. In all three, breath and timing need to be in play, along with a "total body involvement" in your technique.
There's an article on my discussion group at http://groups.msn.com/munenmusoryujujitsu
on ki. You can try it and see if it gives you any help.
In my 40+ years of doing martial arts,
I've seen a lot of different ways to squash a bug, but in all that time, I haven't seen a bug that enjoyed it. Dojo practice is not "fighting practice", so until you see the techniques applied for real, your training partners are just "ukes", so you have to take care of them. Attackers, on the other hand, are a different matter for another discussion, but ki is important in all techniques.