These essays need not be and they are not always superficial, because they are brief. They often are the more profound on account of their conciseness, as when they contain a condensed summary of the main principles of the art or science in question, or a brief history of the successive experiments which have issued in some brilliant discovery. These essays are very generally read, even though they are both concise and profound. But they could not be read even though they were less profound than they are, were there not provided a numerous company of readers who are sufficiently instructed in science to appreciate them. That such a body of readers exists in the countries referred to, is easily explained by the existence of public schools and schools of science and technology, by the enormous extension of the knowledge of machinery, engineering, mining, dyeing, etc., etc., all of which imply a more or less distinct recognition of scientific principles and stimulate the curiosity in regard to scientific truth. Popular lectures also, illustrated by experiments, have been repeated before thousands of excited listeners, and the eager and inventive minds of multitudes of ingenious youths have been trained by this distribution of science, to the capacity to comprehend the compact and pointed scientific essay, even though it taxes the attention and suspends the breath for a half-hour by its closeness and severity. The fact is also worthy of notice, that many of the ablest scientists of our times have made a special study of the art of expounding and presenting scientific truth. Some of them have schooled themselves to that lucid and orderly method by which a science seems to spring into being a second time, under the creative hand of its skilful expositor. Others have made a special study of philosophic diction. Others have learned how to adorn scientific truth with the embellishments of an affluent imagination. Some of the ablest writers of our time are found among the devotees of physical science. That a few scientific writers and lecturers may have exemplified some of the most offensive features of the demagogue and the sophist cannot be denied, but we may not forget that many have attained to the consummate skill of the accomplished essayist and impressive and eloquent orator.