Betts, G. H. (1923). Intelligence and its measures. In G. H. Betts, The mind and its education (pp. 259-277). New York, NY, US: D Appleton & Company.
http://dx.doi.org/10.1037/13538-015
Not the least of the contributions made by original nature to the individual is that of general intelligence. The Binet-Simon-Terman intelligence tests, the Army intelligence tests, and school achievement tests are discussed. Individual differences in intelligence are discussed. Just what is it that makes one person intelligent and another unintelligent? It is probably not possible to explain fully all the factors that enter into intelligence, but some of them are fairly evident: the capacity to receive and respond to impressions lies; the ability to conserve and make use of past experience; the power to give continued attention and sustained effort; and the capacity to be interested in and curious about factors of the environment. (PsycINFO Database Record (c) 2016 APA, all rights reserved)