Nicolaas Hartsoeker, a Dutch philosopher, born in Gouda, March 20, 1656, died Dec. 10, 1725. He was intended for the church, but devoted himself to scientific pursuits. One of his earliest inventions was an improved form of object glasses for microscopes, which enabled him to discover animalcules in the animal fluids, on which a new doctrine of generation was formed. Subsequently in Paris he succeeded in manufacturing object glasses for telescopes superior to any previously made. An account of these discoveries was published in the Journal des Savants of Paris by Huygens, and in 1694 Hartsocker published there an Essai de dioptrique, followed in 1696 by Principes de physique. He afterward returned to Holland, and while there was introduced to the czar Peter, who endeavored without success to induce him to settle in St. Petersburg. After filling for several years the professorship of mathematics in Dus-seldorf, ho retired to Utrecht. One of his last works was Recueil de plusieurs pieces de physique, in which the system of Newton was assailed with more violence than force.

Previous to this he published his lectures under the title of Conjectures physiques (Amsterdam, 1706-8), and a number of other works, many of a controversial nature.