son, its interest being due not alone to its valuable contents, but quite as much to the form in which they have been put by their illustrious author. When the present Monthly was started, surprise was expressed in various quarters at the broad scope of its discussions, which it was said went far beyond the legitimate meaning of our title. Science being considered as a kind of tough and forbidding knowledge belonging to laboratories, observatories, and apothecaries' shops, popular science was regarded as the same kind of knowledge loosely stated in common language. At the outset we rejected this view as narrow and false, holding that science, instead of pertaining to certain things, consists in a method of knowing, which applies to all things that can be known, and that popular science must be equally comprehensive. Science itself being progressive, its great army of workers is constantly engaged in extending and correcting it by numberless processes of original investigation, while it is the office of popular science to bring its conclusions, applications, and results, into the sphere of common thought. Learned men long neglected the duty they owed to the public to clothe the result of their labors in authorized and acceptable forms for general use, and the consequence was that this work was done by incompetent hands, and degenerated into mere amusement and recreation; but, with the progress of liberal opinion, the diffusion of education, and increasing respect for the rights and welfare of the people, eminent men of science have turned their attention seriously to the task of embodying their ideas in popular form.
In his introduction to the present volume, Prof. Tyndall remarks: "One evening during my residence in Berlin, my friend Dr. Du Bois-Reymond put a pamphlet in my hands, remarking that it was the 'production of the first head in Europe since the death of Jacobi,' and that 'it ought to be translated into English.'" That "first head in Europe" was on the shoulders of Helmholtz, and the pamphlet was his celebrated essay on the "Interaction of the Natural Forces," which has been extensively circulated in this country, and is one of the most elegant and popular expositions of the doctrine of the "Conservation of Force" that has appeared in any language. The first complete work of Prof. Helmholtz in English is the volume now issued, consisting of popular lectures on scientific subjects. Speaking of these lectures in his preface, the author says: "If I may claim that they have any leading thought, it would be that I have endeavored to illustrate the essence and the import of natural laws and their relation to the mental activity of man. This seems to me the chief interest and the chief need in lectures before a public whose education has been mainly literary." It is gratifying to note that this statement of the chief aim of popular science entirely coincides with the view presented in the prospectus of The Popular Science Monthly. It is not the illiterate that are to be addressed, but the classes that have received such cultivation as the prevailing educational system affords, while the development and illustration of natural laws in their bearing upon the higher nature and elements of man is the ultimate and most important end to be attained.
Hermann Ludwig Ferdinand Helmholtz was born at Potsdam in 1821. He studied medicine, and was at first military physician and afterward assistant at the Astronomical Museum at Berlin in 1848. From 1849 to 1852 he was Professor of Physiology in the University of Königsberg. He became Professor of Physiology at the University of Bonn in 1855, and in 1858 accepted the physiological chair in the University of Heidelberg. He is now reestablished in Berlin as professor in the university of that city. Prof. Helmholtz has attained a recognized preëminence in three great departments of knowledge—physiology, physics, and mathematics. He began with the study of physiology, but, finding that to be dependent upon physics, he proceeded to master the physical field. But here, finding again that physics depends upon mathematics, he pushed on to the conquest of this department of science. His great works are on "Physiological Optics" and "The Physiology of Audition," and, by his thorough acquaintance with physics and mathematics, he has greatly enriched and extended our knowledge of the science of these higher senses. Prof. Helmholtz's intellect is characterized by great breadth and
