Directions on the right of the illustration refer to the dimensions of the original drawing.

Line Width of Letters

Approx. Desig- Width,

nation Sample Line inches

W-1

iV-2 W-2

0.025

0.017 0.017

'^.

/

'W

\,

Ov^^

\v

.:^

/M^;^;

^

j^ritr^

^

Potiiion of Slide Number

Lib«l (Thumb Spot)

Gnd Rulintt Break at Labels and Symbols

Oosed Symbols for Observed Points

Same Source as A Above

C. Suggested Practices for Charts for Lantern Slides.

1. Reduced '/i from oritjinal cut.

2. Cut was reduced from drawing 6 x

^Va", including margins.

LANTERN SLIDES

Science Service, Inc., Washington. D. C.

Microfilm Reader.

photo-

Reading by projection is of increasing importance in the larger public libraries, universities, scientific institutions, and business organizations where research is carried on. A typical machine for this purpose is illustrated at the left.

Through the cooperation of the more important libraries throughout the world, immense resources are rapidly being made available to the research worker by this cheap and convenient method. Prices vary somewhat but complete books may usually be copied for from one to three cents a page. Work in color is slightly more expensive, but sometimes invaluable. The photographing of old documents and manuscripts on infra-red film frequently brings to light erasures, changes, and sometimes forgeries hitherto unsuspected.

The American Documentation Institute, Washington, D. C, in cooperation with the United States Department of Agriculture, public libraries, and other research institutions, acts as a clearing house for much of this Bibliofilm Service.

Publication by this film method is also coming into use for research material which does not require a large edition. The economy and convenience of this can easily be seen. The use of Microcolor film by Bibliofilm Service adds to the scope and value of research extract copying, since colored specimens and objects as well as illustrations may be reproduced and used either for individual reading or projected on a wall screen for class or lecture use.