Immediately a discovery is effected it is made public, and is afterwards incorporated in the ordinary text books of science, ready for the use of inventors; and in this way such books have become filled with valuable knowledge acquired by researches in past times. All this knowledge (which has cost millions of pounds and a vast amount of intellect and labour) has been given by its discoverers freely to the nation. Some idea of the number of scientific {9} researches which have been made since the year 1800, may be obtained from the fact, that a mere list of their titles, with the names of the authors, occupies eight large quarto volumes, of about one thousand pages each, compiled and published at a cost of about ten thousand pounds, by the British Government and the Royal Society. In discovery we search for new phenomena, their causes and relations; in invention we seek to produce new effects, or to produce known effects in an improved manner. The objects of the scientific discoverer are, new truth and greater accuracy; whereas those of the inventor, are increased usefulness and economy of results. The ancients classed inventors with the gods, because they considered them great benefactors to the human race. Discoverers may properly be viewed as priests and prophets of truth, because they both reveal new knowledge to mankind, and predict with certainty coming events. A man cannot usually invent an improvement unless he possesses scientific knowledge, and, for that knowledge he must in nearly all cases resort to a scientific book or teacher. The great practical value of new scientific knowledge is proved by the fact, that when scientific discoveries are published, there are numerous inventors and practical men, who immediately endeavour to apply them to useful purposes. Since the first application of coal-tar to the production of dyes, every discovery in that {10} branch of chemistry has been closely watched for a similar purpose.