6 Henry Quastler 



a certain status. In biology, economics, political science, esthetics, linguistics, 

 information theory has interested many people, but the active users are only 

 a handful. 



II. THE REPRESENTATION OF INFORMATION 



'One if by land, two if by sea.' Paul Revere and his fellow citizens did 

 not know information theory, but they knew and utilized what is at the basis 

 of information theory, namely, the principle of the representation of intelligence. 

 The Paul Revere code is not quite up to modern standards, but it has the 

 essential properties: 



(i) The news concerning the road of approach of the enemy was translated 

 into another kind of intelligence, nam.ely, lights hoisted on a steeple; this 

 translation is useful because it transforms a hard-to-broadcast piece of intelli- 

 gence into one which is easily broadcast; 



(ii) the range of all possible events was subdivided into categories of 

 interest. The code could have been reduced to one which indicated only the 

 enemy's arrival. It could have been expanded into one conveying more 

 accurately the direction of approach, or signalling the enemy's strength and 

 other details of possible interest. In this case, a more complicated code would 

 have been necessary, and this would have increased the possibility of misunder- 

 standings. Proper economy of categorization is an important feature in 

 representing information ; 



(iii) the representation employed a code previously agreed upon. No 

 light meant no enemy approaching, one indicated land, two indicated sea. It 

 seems that no agreement was made concerning simultaneous approach by land 

 and by sea, but the message 'three lights' would have been correctly interpreted 

 by all concerned. 



Possibilities of Representing Information 



There is no limit to the number of possibilities of representing one kind of 

 information by another. (It may be observed that the term 'information' covers 

 more ground than the word 'intelligence'. Generally, the word intelligence is 

 restricted to conscious informiation.) The only condition for representation is 

 that a complete system of translation, a code, be agreed upon. The limitations 

 are set only by the ability to discriminate information to be represented, by the 

 ability to produce accurately a desired representation, and by the range of 

 the code. 



Representation is not restricted to discrete categories of intelligence. A 

 continuum of information or state of affairs can be represented by a physical 

 continuum such as a range of voltages or the rotation of a shaft. Any kind of 

 information, discrete or continuum, can be represented by the charges in an 

 electron tube, by the magnetization of a spot on a metallic surface, by the 

 deflection of the beam of a cathode ray tube, by a hght falling upon a photo- 

 graphic emulsion, and so forth (7). 



It is possible to represent not only data, but also operations on data. On a 

 slide rule, numbers, a kind of intelligence, are represented on scales by marks, 

 which is a form of encoding. The operation of multiplication is encoded by 

 positioning the slide and the indicator, and decoded by the act of reading from 



