PHENOMENA OF DEW. 297 



fent; but as the partition is more heated than if it were not 

 prefent, there is no effecl, and the totality of the double glafs 

 armed within, is in the Came cafe with that unarmed; it there- 

 fore accumulates neither more nor Iefs humidity. 



A fecond armour on the plate of glafs will caufe the pheno- 

 mena to re-appear ; a fecond plate of glafs on this new armour 

 will again make it difappear, &c. For as long as the fymme- 

 trical glafs (hall have the interior armours, the caufes of heat 

 and cold will be found in equilibrio; but an additional armour 

 will necefTarily deftroy the balance, and the heated glafs will 

 not attrad humidity; which explains the facts of § 27. III. 

 A. B. C. D. &c. 



D. If the glafs be armed on both fides (§ 7), as ft would not 

 then be expofed to the air, either on the cold or warm fide, 

 it feems that it ought to attract as much humidity on the ar- 

 mours as on the reft of the partition. But though the glafs ex- 

 crcifes its adtion through the metal, this is neverthelefs an ob- 

 stacle which diminifhes its force ; humidity in this cafe will not 

 then be fo ftrongly attracted by the doubly armed glafs as by 

 the part perfectly unarmed, &c. 



CONCLUSION. 



Thefe obfervations are not only interefting, but they appear Conchifioa, 

 to eftablifli an important point in philofophy ; namely, that 

 glafs exercifes its attraction for the humidity (which has a tendency 

 to be depofited from the air) through metals. See likewife § § 

 19 and 26 for the generalization of thispropofition. 



EXPLANATION OF THE FIGURES. 



Fig. 1, Plate XV. relates to Art. 4- of the abftraft. A is Explanation of 

 the interior reclangle more deeply (haded than the reft of the e gures * 

 fquare, which fignifies that it is more moiftened. B is the 

 place correfponding to the exterior rectangle, with its furround- 

 ing part reprefented white, becaufe dry. 



Fig. 2 relates to § § 7 and 8. 



Fig. 3, 4, 5, 6, 7, relate to Art. 7 and 9. I c fignifies 

 interior fide hot ; E f, exterior fide c»ld. The lines more deeply 

 /haded reprefent the fe&ion of the metallic leaves ; the white 

 lines reprefent the fection of the glafs, and the dotted ihades 

 reprefent drops of dew or moifture. 



Fig. 8 relates to Art. 11, 



SCIENTIFIC 



