1．The Preservation of fossils 1
2．Communal Roosting of Birds 10
3．Adaptations of Desert Animals 20
4．The Cause of Air Pollution 29
5．Transportation of the Nineteenth Century 39
6．The Development of Microscopes 48
7．The American Folk Art Portraiture 58
8．The Theory of Plate Tectonics 69
9．Changes in American Diet 79
10．The Story of an Accomplished Woman 89
11．Cohesion and Adhesion 97
12．Diversions of Early Settlers 105
13．Schooling and Education 115
14．The Value of Beads 125
15．The Policy of Rental Control 135
16．Galaxies of the Universe 148
17．Parasitism of Ants 159
18．Iron Used in Architecture 169
19．The Development of a Fungicide 182
20．The Igneous Rock of the Earth 191
21．Development of the Trumpet 202
22．The Arctic and the Antarctic 210