Johann Kepler, the great German astronomer, was a contemporary of Tycho Brahe and Galileo with both of whom he was in correspondence. Kepler’s contributions to science were of the utmost importance. It was he who established the two cardinal principles of modern astronomy—the laws of elliptical orbits and of equal areas. He also enunciated important truths relating to gravity. In spite of the backward condition of mechanical knowledge, he attempted to explain the planetary evolutions by a theory of vortices closely resembling that afterwards adopted by Descartes. He also prepared the way for the discovery of the infinitesimal calculus. His literary remains were purchased by Catherine the Second of Russia and were only published during the latter half of the Nineteenth Century. It is impossible to consider without astonishment the colossal amount of work accomplished by Kepler, despite his great physical disabilities. When only four years old an attack of small-pox had left him with crippled hands and eyesight permanently impaired. His constitution, already enfeebled by premature birth, had to withstand successive shocks of illness.

Flamstead, the great British astronomer, was obliged to leave school in consequence of a rheumatic affection of the joints. It was to solace his enforced idleness that he took up the study of astronomy. The extent and quality of his performance is almost unbelievable when one considers his severe physical suffering.

Nicholas Saunderson lost his sight before he was twelve months old, yet he became professor of mathematics at Cambridge. He was an eminent authority in his day, an original and efficient teacher and the author of a book on algebra. His knowledge of optics was remarkable. “He had distinct ideas of perspective, of the projection of the sphere, and of the forms assumed by plane or solid figures.”

D’Alembert was not only a mathematician but also a philosopher of the highest order. He was made a member of the French Academy at the age of twenty-four. He was so frail that his life was continually despaired of and he remained a valetudinarian to the end.