Excerpt from Lives of the Most Eminent Literary and Scientific Men of Italy, Spain, and Portugal, Vol. 2

In a memoir so brief and general as the present, it would be out of place to discuss the history of this ex traordinary invention. We have no hesitation in as serting that a method of magnifying distant objects was known to Baptists Porta and others but it seems to be equally certain that an instrument for producing these effects was first constructed in Holland, and that it was from that kingdom that Galileo derived the knowledge of its existence. In considering the contending claims, which have been urged with all the ardour and partiality of national feeling, it has been generally overlooked, that a single convex lens, whose focal length exceeds the distance at which we examine minute objects, performs the part of a telescope, when an eye, placed behind it, sees distinctly the inverted image which it forms. A lens, twenty feet in focal length, will in this manner magnify twenty times and it was by the same principle that Sir William Herschel discovered a new satellite of Saturn, by using only the mirror of his forty-feet telescope. The instrument presented to prince Maurice, and which the marquis Spinola found in the Dutch Optician's shop, performing the part of a philosophical toy, by exhibiting a magnified and inverted image of a distant weathercock, must have been a single lens such as we have mentioned, or an astronomical telescope consisting of two convex lenses. Upon either of these suppositions, it differed entirely from that which Galileo constructed; and the Italian philosopher will be justly entitled to the honour of having invented that form of the telescope which still bears his name.

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