HISTORY OF PHYSICAL ASTRONOMY.
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elevated parts of tlie city, whence, by looking through it, they surveyedthe various objects of the surrounding landscape with inexpressible sur-prise and delight. During the whole period of his residence at Venice,which extended to a month, he was besieged from morning to night bycrowds of the inhabitants, all eager to have a peep through the won-derful glass. He had not yet divulged the secret of his invention, but,with his wonted liberality, he now communicated it to the public, and, atthe suggestion of one of his friends, he presented the instrument itselfto the Doge Leonardi Deodati, who accepted it from him, sitting in fullcouncil. He accompanied it with a paper, in which he gave an explana-tion of its construction, and of the important purposes to which it mightbe applied both on land and at sea. The Senate indicated their appre-ciation of this novel compliment which Galileo paid to the chief magis-trate, by increasing his salary as lecturer in the University of Padua to 1000florins, and appointing him to his office for life.
Galileo ’s object now was to construct a telescope of superior magnifyingpower. This he found to be a task of very difficult accomplishment, forthe art of grinding and polishing lenses was then in its infancy. We haveseen that at his first trial the instrument made objects appear three timesnearer and nine times larger ; in other words, it amplified three times inlinear dimensions, and nine times in superficies. Soon afterwards he madeanother instrument which magnified sixty times in surface; and finally,sparing neither application nor expense, he succeeded in executing an in-strument of such excellence as to represent objects almost 1000 timeslarger, and above 30 times nearer, than they appeared to be by the naturalpower of the eye *.
He points out a simple method of determining by experiment themagnifying power of the instrument. “ Place,” says lie, “ upon a wall at acertain distance, two disks, one of which you will observe with thetelescope and the other with the naked eye. If the disk seen throughthe telescope appear equal to the external one, the magnifying powerof the instrument is in the proportion of the two disks. If they do notappear equal, the external disk must be enlarged or diminished until thisresult takes place, and then the magnifying power will be, as alreadymentioned, in the proportion of the two disks.”
Galileo ’s best telescopes did not magnify more than thirty-two or thirty-three times. Previous to the invention of achromatic object-glasses, thiswas the highest magnifying power that was attainable with telescopes ofthe form of construction employed by him and his contemporaries. Thetriumphs of genius are signally illustrated in the multitude of beautifuldiscoveries which Galileo achieved by the aid of his little perspective.Whatever claims other individuals [may possess to the original inventionof the telescope, the merit of applying it to the great purposes of pli}'-sical science must be awarded, with acclamation, to the illustriousphilosopher of Italy .
The telescopic discoveries of Galileo exercised such a witheringinfluence upon the ancient philosophy, that many of its adherents, in theheight of their mortification, took refuge in absolute incredulity, and, withabsurd pertinacity, refused to assure themselves, by actual inspection, ofthe reality of the phenomena thus revealed for the first time to mortaleyes. “ Oh! my dear Kepler,” says Galileo , in one of his letters to that