Presented at the National Association for Research in Science Teaching meeting, Chicago Ill., April 6, 1972. Sponsored by the Educational Resources Information Center of the United States Office of Education and The Ohio State University. This publication was prepared pursuant to a contract with the Office of Education, United States Department of Helth, Education, and Welfare. Contractors undertaking such projects under Government sponsorship are encouraged to express freely their judgment in professional and technical matters. Points of view or opinions do not, therefore, necessarily represent official Office of Education position or policy.