The mere fact already noted that close binary systems exist in considerable numbers is sufficient to make it probable that a certain proportion of these stars would have their orbit planes turned so nearly edgewise toward the earth as to produce eclipses, and corresponding to this probability there are already known no less than 15 stars of the Algol type of eclipse variables, and only a beginning has been made in the search for them.
"A Text-Book of Astronomy"
George C. Comstock
An experimentally verifiable system must contain space-time variables, for which can be substituted the here and now of the experimenter's immediate experience.
"The Approach to Philosophy"
Ralph Barton Perry
At the Cirencester Agricultural College, England, about 1860, broccolis were produced, with other variables, directly from seeds of the wild cabbage.
"The Cauliflower"
A. A. Crozier