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BURNING MIRRORg.

axis into the focus. We are informed by historians, thatArchimedes , by means of reflecting; mirrors of this, or someother description, burned the Roman fleet, under the com-mand of Marcellas, lying before, and laying siege to Syracuse .The machines then used for those purposes, no body ques-tions, were concave, and had their power by reflection; itbeing pretty evident that the ancients were unacquaintedwith the refracted focii of convex glasses. Yet, it has beenobserved by M. de la Hire, that in the Clouds of Aristo-phanes, Strepsiades tells Socrates of an expedient hehad to pay his debts, by means of a round transparentstone or glass, used.in lighting of fires ; by means of whichhe intended to melt his bond, which in those days werewritten on wax. The glass here used to light the fire andmelt the wax, M. de la Hire observes, could not be con-cave, as a reflected focus coming from below, inwards,would have been improper for the purpose. The oldscholiast upon Aristophanes confirms, the same sentiment.Pliny mentions globes of glass and crystal, which being ex-posed to the sun, burnt the clothes and flesh upon people’sbacks; and Lachinilius adds, that a glass sphere full ofwater, and held in the sun, lighted the fire even in thecoldest weather; which, besides proving the effect of convexglasses, also informs us the ancients knew their use, atleast as far as simple reflection was concerned.

That they must also have been acquainted with the mag-nifying power of glasses, contrary to the generally receivedopinion, is • evident, from considering the delicacy andminuteness of some of their works; upon this point we aresatisfied, from what appears in a former part of our labours;because we know the works alluded to could not have beenperformed without optical aid. Those who so strenuously denythis knowledge to the ancients, should reflect upon the lengthof time which elapsed between the discovery of spectaclesand telescopes, being upwards of 300 years, and then theywould not have so partial a feeling for the excellencies oftheir own day, as to aflirm that sciences, arts, and know-ledge, were concealed from the wise of antiquity, and areonly revealed to themselves and their sagacious and sapientcontemporaries!

The fact will appear upon examination to be thus: theprinciples of general science and universal art were betterunderstood by the learned of antiquity than they are amongthose of the moderns; the latter, perhaps, possess someslight advantage over the former in this, that their workmenaided by subsequent inventions, have the means to executethe directions of the scientific with more accuracy, conse-