Having determined a person's scope of attention, you may want to test his accuracy in details as compared with other men. To conduct such an experiment dictate a statement which will form one typewritten letterhead sheet. This statement should comprise facts and figures about your business of which the subjects to be tested are supposed to have accurate knowledge. After this original page is written, have your typist write out another set of sheets in which there are a large number of errors both in spelling and figures. Then have each of the persons to be examined go through one of these sheets and cross out all the wrong letters or figures. Time this operation. The man who does it in the quickest time and overlooks the fewest errors, naturally ranks highest in speed and accuracy of work. [Sidenote: _Other Business Applications_] Look into your own business and you will undoubtedly find some department, whether it be store decoration, office furnishing, window dressing, advertising, landscape work or architecture, in which a systematic application of a knowledge of sensory illusions will produce good results. CHAPTER IV INWARDNESS OF ENVIRONMENT [Sidenote: _Factors of Success or Failure_] The aspect of the sense-perceptive process that deals with the relation of mind to environment is of greatest practical value. Look at this subject for a moment and you will see that the world in which you live and work is a world of your own making. All the factors of success or failure are factors of your own choosing and creation. If there is anything in the world you feel sure of, it is that you can depend upon the "evidence of your own senses," eyes, ears, nose, etc. You rest serene in the conviction that your senses picture the world to you exactly as it is. It is a common saying that "Seeing is believing." [Sidenote: _Should Seeing Be Believing?_] Yet how can you be sure that any object in the external world is actually what your sense-perceptions report it to be? You have learned that a countless number of physical agencies must intervene before your mind can receive an impression or message through any of the senses. Under these conditions you cannot be sure that your impression of a green lamp-shade, for instance, comes through the same sort of etheric and cellular activities that convey a picture of the same lamp-shade to the brain of another. If the physical agencies through which your sense-impressions of the lamp-shade filter are not identical with the agencies through which they pass to the other person's brain, then your mental picture and his mental picture cannot be the same. You can never be sure that what both you and another may describe as green may not create an entirely different impression in your mind from the impression it creates in his.