To keep society as regards science in healthy play, three classes of workers are necessary:  Firstly, the investigator of natural truth, whose vocation it is to pursue that truth, and extend the field of discovery for the truth’s own sake and without reference to practical ends.  Secondly, the teacher of natural truth, whose vocation it is to give public diffusion to the knowledge already won by the discoverer.  Thirdly, the applier of natural truth, whose vocation it is to make scientific knowledge available for the needs, comforts, and luxuries of civilized life.  These three classes ought to co-exist and interact.  Now, the popular notion of science, both in this country and in England, often relates not to science strictly so called, but to the applications of science.  Such applications, especially on this continent, are so astounding—­they spread themselves so largely and umbrageously before the public eye—­that they often shut out from view those workers who are engaged in the quieter and profounder business of original investigation.

Take the electric telegraph as an example, which has been repeatedly forced upon my attention of late.  I am not here to attenuate in the slightest degree the services of those who, in England and America, have given the telegraph a form so wonderfully fitted for public use.  They earned a great reward, and they have received it.  But I should be untrue to you and to myself if I failed to tell you that, however high in particular respects their claims and qualities may be, your practical men did not discover the electric telegraph.  The discovery of the electric telegraph implies the discovery of electricity itself, and the development of its laws and phenomena.  Such discoveries are not made by practical men, and they never will be made by them, because their minds are beset by ideas which, though of the highest value from one point of view, are not those which stimulate the original discoverer.

The ancients discovered the electricity of amber; and Gilbert, in the year 1600, extended the discovery to other bodies.  Then followed Boyle, Von Guericke, Gray, Canton, Du Fay, Kleist, Cunaeus, and your own Franklin.  But their form of electricity, though tried, did not come into use for telegraphic purposes.  Then appeared the great Italian Volta, who discovered the source of electricity which bears his name, and applied the most profound insight, and the most delicate experimental skill to its development.  Then arose the man who added to the powers of his intellect all the graces of the human heart, Michael Faraday, the discoverer of the great domain of magneto-electricity.  OErsted discovered the deflection of the magnetic needle, and Arago and Sturgeon the magnetization of iron by the electric current.  The voltaic circuit finally found its theoretic Newton in Ohm; while Henry, of Princeton, who had the sagacity to recognize the merits of Ohm while they were still decried in his own country, was at this time in the van of experimental inquiry.