Contrary to his expectation...

Contrary to his expectation, he discovered that in the place where light did not reach the eye there was a factor, which caused the silver chloride to darken. Later still, scientists found out that the changing of the colour of the skin on exposure to sunlight was due to the chemical influence of this radiation. It thus became certain that beyond violet light there was another radiation, which was invisible, and it was named ultra-violet. e. One more example is inaudible sounds.

There are many sounds, which we do not hear. These are called supersonic sounds, and we discover their existence by examining their effects; they are used in medicine and technology. f. Intelligence is another case of such nature. All of us are aware of ourselves, i.e.

we perceive that we exist, and we can also arrive at concepts in a gradual manner concerning matters outside ourselves which we explain by this kind of statement: 'I solved the most difficult mathematical problem.' 'I pondered a lot over such-and-such a theory until I came to the conclusion that it was correct.' Also, man is aware of his own knowledge, i.e. he knows that he knows.

Intelligence is not something visible or audible in the sense that man can see it with his eyes or hear it with his ears, but in fact, although it is intangible, everyone finds it in himself in addition to the powers of sight and hearing and the other external faculties. Other people cannot learn about my intelligence through the five senses. Instead they must deduce its existence from the effects it produces.

For example, when a scientist is expounding on a problem, it becomes clear that he has understood it. Also, if we ask a scientist if he is familiar with mathematical problems or not, and he says that he is informed about them, we understand that he is aware of his own understanding and knowledge, i.e. he knows that he understands the problems of mathematics.[^1] The Constructs of the Mind People can construct in their own minds any form that they wish.

For example they can build a tower similar to the Eiffel tower whose construction in the-external world required many years, a thousand sorts of different building materials and substances, and hundreds of workers: this can be built in the mind in an instant. Maybe thousands of similar ones can be built, and it is possible to imagine in the mind things, which have no existence in the outside world at all. We may create a monster with many heads, hands and feet.