IOWA ACADEMY OF SCIENCE xi 
Page 
A Study of the Cherts of the Osage Series of the Mississippian System 173 
Evidence Favoring the Radioactive Disintegration of Sodium .as an Element. 175 
The Effept of Rupture by Abrasion on the Electrical Conductivity of 
Selenium 179 
A New Apparatus for Measuring Small Intervals of Time Independent of 
Clock or Chronograph 185 
A Method of Determining Whether the Restoring Torque is Proportional 
to the Torsional Strain During Vibration of a Torsional Pendulum 189 
The Occurrence of Melanism in the Broad Winged Hawk 191 
Notes on the Food of the Black Crowned Night Heron in Captivity 193 
A Remarkable Flight of Broad Winged Hawks 195 
The Harvest Mouse in Iowa 197 
Food Habits of the Red Tailed Hawk, Cooper’s Hawk, and Sparrow Hawk. . .199 
Notes on a Collection of Mammals from Northwestern Iowa 203 
Contribution to the Herpetology of Iowa, II 207 
A Study in Insect Parasitism 209 
The Source of the Chromaffin Cells of the Adrenals of the Pig 215 
A Systematic Outline of the Reduviidae of North America 217 
Early Iowa Locality Records 253 
