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events ; thefe fignals by degrees were applied to an alphabetical 

 arrangement, M'hich is minutely defcribed by Polybius. The 

 ancients had a much more ingenious contrivance, that contains 

 the principles of all the improvements v^^hich have fince been 

 made on this fubje£t. The Clepfydra was ufed like an hour-glafs, 

 to count time; it confifled of a tall veffel with a hole at the 

 bottom, through which water paffed flowly. The defcent of the 

 furface of the water marked the lapfe of time : Two fimilar 

 Clepfydras, with the addition of a floating gauge in each, on 

 which different fentences were infcribed, were fet in motion at 

 once by a fignal, and were flopped by another fignal when the 

 fentence on the floating gauge defcended to a certain index. 

 But a ftill more compendious method of communication was 

 fuppofed to exift in the i6th century. It vras reported that 

 two magnetic dials, with the four-and-twenty letters infcribed 

 on their circumference, would by means of felf-moving hands 

 point to the letters which the correfpondents meant to indicate. 

 The great Bacon believed in thofe fympathetic dials, and the 



learned. 



«< So on her fea-girt tower fair Hero ftood 

 •' At parting day, and marked the dafliing flood ; 

 " While high in air the glimmering rocks above, 

 " Shone the bright lamp, the pilot ftar of love — 

 " With robe outfpread the wavering flame behind 

 " She kneels, and guards it from the fhifting wind ; 

 " Breathes to her goddefs all her vows, and guides 

 " Her bold Leander o'er the duflcy tides." 



Dr. Darwin's Botanic Garden. 



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