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PRINTED MATERIALS, MAPS, CHARTS 



study by Hoffman (26) of reading continued 

 for four hours, blink rate, together with other 

 aspects of eye movements, showed signifi- 

 cant changes. But several investigators, 

 evaluating the bhnk rate experimentally, 

 have failed to find it a satisfactory measure 

 (4, 8, 9, 31, 52, 53.) It is thus seen that, 

 though blink rate may in some circumstances 

 reflect the conditions of reading, the lack 

 of consistent results when this index is used 

 by different workers makes it difficult to 

 evaluate any single set of data. This con- 

 troversy has been covered in an analytic 

 review by Bitterman (6). 



The well-known capacity of the human 

 organism to compensate for unfavorable con- 

 ditions, and especially the tendency to do 

 so in brief test situations that are recognized 

 as tests by the subjects, often results in 

 uniformly high performance scores when con- 

 ditions are 'uddely varied. This gives rise 

 to two problems. The first is the problem 

 of getting an index of the energy cost per 

 unit of work output. In the case of visual 

 work the measurement of associated in- 

 voluntary responses is a step, at present of 

 uncertain value, in this direction. The need 

 for dependable measures for this purpose is 

 generally recognized. 



The second problem is that of determining 

 the consequences to the organism of a given 

 level of energy cost. The implicit assump- 

 tion often made is that the optimum cost for 

 a given work output is the minimum cost. 

 This assumption seems safe enough when the 

 task is arduous or when the subject is work- 

 ing near the limJt of his tolerance or en- 

 durance. But when the work is light and 

 other conditions are not conspicuously un- 

 favorable, the situation is less clear. There 

 are three possibihties: (1) that the more 

 costly way of doing a task produces cumu- 

 lative impairment over a period of a day or 

 several days, (2) that the additional energy 

 loss and discomfort is negligible, relative to 

 the total demands on the organism and to the 

 capacities of the particular organs involved, 

 or (3) that the higher energy output is favor- 



able in terms of some secondary criterion 

 such as physical tonus or health. When 

 immediate cost can be satisfactorily meas- 

 ured, the consequences to the organism will 

 need to be studied as a separate problem. 



Typographical Factors 



With these considerations in mind we turn 

 to studies of typographical variables. Such 

 studies have quite generally been subject 

 to the limitation that the reading periods 

 involved were brief. More studies of pro- 

 longed reading are needed to verify the as- 

 sumption now tentatively made that any 

 effects appearing in brief reading periods 

 will appear to at least as great an extent in 

 longer periods.^ 



A few words about details of typography. 

 The unit of measure for type sizes is the 

 "point." A point is 0.0138 inch, or 0.351 

 millimeter. Three-point type is about the 

 smallest that can be read at 14 inches under 

 favorable conditions. With occasional ex- 

 ceptions, newspapers are printed in 7- or 

 8-point, jounals in 9- to 11-point, and text- 

 books in 10- to 12-point. The point size 

 gives exact dimensions for the type body 

 only. Dimensions of the letter mounted on 

 the body will vary with the type face. Line 

 width (the printer's term for line length) is 

 measured in picas. One pica is 12 points 

 (0.166 in. or 4.21 mm). Single column text- 

 book lines are usuallj^ between 19 and 24 

 picas. Leading, the space between lines, 

 varies somewhat with type size and other 

 factors, but most textbooks are set with 2- 

 point leading. The present volume is pre- 

 pared in 10 point type, with 16 picas to the 

 column and 2 point leading. 



Many type faces have been designed, but 

 a relatively small number of them are widely 

 favored for ordinary printing in books and 

 journals. Type faces differ, not only in 



factors has been covered in a review for the Air 

 Force by Young (59). 



2 Reading periods up to 10 or 15 minutes are 

 here classified as "short," and periods from one- 

 half hour to several hours as "long." 



