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to the planets. By their vapours the water spent in 

 them, may be supplied and recruited. All vegetables 

 grow from fluids. But when they putrefy, great part of 

 them turn into dry earth : hence the quantity of dry 

 earth must continually increase, and the moisture of the 

 globe decrease. Add to this, that immense quantities of 

 watry vapours, are continually arrested in the polar 

 regions, and falling down form mountains of eternal 

 snow, and rocks of ice that thaw no more. By both 

 these means the moisture of the planets continually de- 

 creasing, must in process of time, entirely fail, if it had 

 not a seasonable supply from some other part of the uni- 

 verse. Comets therefore are so far from being super- 

 flous, much more from being blemishes in the universe, 

 that it may be doubted whether either the animals or ve- 

 getables of the earth could long subsist without them. 



And indeed, if the uses assigned to the comets, by Sir 

 Isaac Newton be real, as they are not improbable, name- 

 ly the, supplying the deficiency and expenses of all sorts 

 of fluids necessary to the earth : I mean not only light 

 and heat to the sun, and watry vapours to our atmos- 

 phere, but the most subtle, most useful, and necessary 

 part (towards life and vegetation) to the air ; then 

 these wandering, frightful bodies, may be justly con- 

 ceived joining in. the chorus, arid loudly resounding the 

 common hallelujah. 



But the astronomy of comets, says Mr. Brydon is 

 clogged with very great difficulties, ,and even some 

 seeming absurdities. It is difficult to conceive, that 

 these immense bodies, after being drawn to the sun, 

 with the velocity of a million of miles in an hour, when 

 they have at last come almost to touch him, should 

 then fly off from his body, with the same velocity they 

 approached it, and that too, by the power of this very 

 motion, that his attraction has occasioned. The demon- 

 stration of this, I remember is very curious and ingeni- 

 ous* but 1 wish it may be entirely free from sophistry. 

 No doubt, in bodies moving in curves round a fixed cen- 

 tre, as the centripetal motion Increases, the centrifugal 



