5-20

HISTOKY OF PHYSICAL ASTRONOMY.

mitted to trial, it was cordially approved of by the Committee of theirHighnesses. It appears, then, that this ingenious individual was the firstperson who executed the binoculm, an instrument the invention of whichhas been usually ascribed to De Pdieita. Lipperhey doubtless fell uponthe construction of the telescope by combining together lenses in variousways, as we may easily conceive that an optician might be induced to do-.Attempts have been made to depreciate the merit of the Dutch inventor,on the ground that his discovery was made by chance. There exists,indeed, no reason to suppose that he was acquainted with the principles,whether mathematical or physical, upon which the construction of thetelescope depends, or that he was indebted to a knowledge of those prin-ciples for the admirable result at which he arrived ; but how few originaldiscoveries or inventions, either in the arts or sciences, have been achievedby the aid of purely theoretical considerations; and, on the contrary,how many have been suggested to their authors by circumstances appa-rently unconnected with the object of their researches, and, therefore, toa certain extent, fortuitous! But, in fact, this circumstance of accidentaldiscovery is no other than the result of that sagacious observation whichdistinguishes one man from a multitude of others, and enables him toselect from the multitude of objects that claim his attention such relationsas possess a character of generality that renders them subservient inextending the conquests of the human mind over the material world.Theory serves to develope principles that have been already established byinduction, and in this manner acts the part of a valuable guide to thediscovery of derivative truths ; but in attempting to penetrate the secretsof nature, or in devising new combinations of principles with a view tothe attainment of any specific end, the mind must rely mainly on its owninnate sagacity.

Galileo lias related the circumstances under which he first becameacquainted with the invention of the telescope, and has also given an accountof his early efforts to construct one of these instruments. Happening tobe in Venice in the month of May, 1609*, he learned in that city that aBelgian had invented a perspective instrument, by means of which dis-tant objects appeared nearer and larger. This report, which was soonconfirmed by a letter he received from Paris, excited an intense interestin his mind, and upon his return to Padua he began to ponder upon theprobable mode by which such an effect could be produced. He discovered, upon the very night of his arrival, that the enlargement of theobject depended upon the doctrine of refraction, and on the following dayhe made his first attempt to execute an instrument upon this principle.Having procured a leaden tube, he fitted in one of its extremities a plano-convex lens, and in the other a plano-concave one, and, having applied hiseye to the concave lens, he was delighted to perceive objects pretty muchmagnified. They appeared to be three times nearer and nine timeslarger. He immediately gave intimation of his success to his friends inVenice, with whom he had been conversing on the subject the previousday. Having succeeded a few days afterwards in making a better in-strument, he joyfully proceeded to Venice, talcing it with him. Theperspective of the Paduan philosopher soon became an object of universaladmiration in Venice. In order to afford the senators of the republic apractical proof of its efficiency, Galileo accompanied them to the more

* This is inferred from the expression “ mensibus abhinc decern fere,” used by himin the Sidereus Nuncius , the dedication of which is dated March, 1610.