This is the John Findley Green Foundation Lecture which Mr. Snow delivered at Westminster College in 1968 dealing with the ominous uneasiness of our times which occasions the title and which he qualifies as ""impalpable."" Before long, however, he itemizes the various and justifiable fears--overpopulation and poverty and famine in the underprivileged countries, war between the dominant U.S. and U.S.S.R. In the space of a short (64) page essay, Mr. Snow can hardly develop these already familiar specters; he merely re-states them in his measured, modulated fashion.