Next would come transmitting the length of our basic time unit. The Fruedenthal system would send, say, a four-second dash, followed by the Lincos sound for “second,” then four dots. Using different dash lengths with corresponding dots and the same sound, it is assumed that the recipients would observe that the length of the dash was proportional to the number of dots. Time concepts (including universal constants) would lead to teaching units of physical length. Upon this foundation of mathematics, time and dimensions, Lincos develops an ingenious and extensive language for a detailed description of earth, its inhabitants and our culture. Lincos, of course, assumes that the listeners are capable of understanding our mathematical concepts and that their reasoning processes are similar to ours. It illustrates one great fundamental difficulty in alien communication: whatever system we use, it has to be devised within the limitations of our one-planet knowledge and experience. The basic principle of association (that is relating numbers to sounds to teach meanings) can be used in other systems. Some form of association, probably beginning with objects and sounds, will be necessary to teach dolphins a human language. One other fundamental means of communication is being considered by scientists. This is the use of geometrical designs or symbols which would then evolve into pictures. It would be most practical in interplanetary communication. A picture, as the Chinese say, is worth a thousand words. In interstellar communication, geometrical figures could possibly be signified by numbers. Thus the pi ratio would denote a circle, three equal successive numbers an equilateral triangle, four equal numbers a square, and so on. From this elementary basis, a method of translating sounds into drawings could be developed. This might take the form of having electrical circuits attached to pens or tiny lights respond to various sounds, thus transcribing the pictures to paper or film. The correct interpretation of whatever messages we receive will be of extreme importance. An error could be disastrous. We need only recall the difficulties we have had in translating early records of our own species to know that interpreting the signals of otherworld beings may be very difficult. Egyptian hieroglyphics were given many translations that contradicted each other before the Rosetta Stone was found. In one example, there were 12 different translations. Should this problem develop, we can only hope that the other-worlders are friendly, tolerant and patient. Then there is the time factor. If, during Project Ozma, a signal had been received and a reply sent, it would have been 22 years before we knew whether our answer had been received. A reply to a message from 80 light-years away received by the new radio telescope being built would take 160 years for confirmation.