PHENOMENA OF DEW. 291 



2. Ill this cafe the preferving property of the metal fre- The metal is not 

 quently extends to a confiderable diftance round, fo that in ^^^^ 

 the midft of the humidity, there is conftituted a zone perfedly place round it. 

 dry and almoft always well terminated. But what is very 

 remarkable is, that when the glafs is moiftened underneath, 



the place anfwering to the metal remains dry; fo that the and even on the 

 influence of the metal ads through the glafs of feveral milli- of P ^hc gUfs!^* 

 metres (or twentieths of an inch) in thicknefs. And we mall 

 foon fee that it extends much farther. 



3. The metal does not in this cafe a£t as a (belter or de- An zU tlonal 

 fence, for if the furface be covered with glafs nothing particu- not S p?oduce°the 

 lar happens. effed of the 



4. Having parted (colle) againft the upper part of a pane °f ^metallic plate 



glafs in a window expofed to the north, and on the inner fur- being pafted on 



face a metallic re&angle ; and on the lower part of the fame th . e f ane °. f ■ 



° * window Witnin ; 



pane externally a ftmilar re&angle, the author obferved> that an( j anotheron a 



when the moifture was condenfed on the inner furface, as d'fterent part 



r . .. ,. ^ r r r •• without ; moif- 



often happens in winter, the inner metal to tar from remaining ture condenfed 



dry, was more moiftened than the glafs, while the furface within fell moft 



correfponding with the external metal was perfectly dry, as metal an d n one 



well as a fquare of feveral lines round about. It was however on the furface 



remarked, that the humidity in the fquare approached much Jw^J^ . mS t0 



nearer the corners of the metal than in the middle of the fides 



of the rectangle. 



3. In the fame arrangement if the humidity was depofited on and moifture 

 the outfide (by cooling) the external metal remained dry, and ^^ X M^ 

 the place correfponding with the internal metal was on the oppofite the in- 

 contrary rather wetter than the reft of the glafs. ter ? al metal > . 



„ri ii • f r it,-,- , • , and n0ne 0n ^ 



4. When the humidity was formed both within and without, outer metal; 

 no moifture was depofited either upon the external metal, or m0lftureon 



' , , . . . both fides did not 



its correiponaent place within. ^e,. the external 



7. When a fmaller rectangle was pafted on the outer fur- metal; or its 



face in the middle of the place correfponding with the inte- ^foiaU external 



rior rectangle, and humidity was depofited internally, the in- metal on the 



terior rectangle was not entirely wetted as it would elfe have J™^* f lte 



been, but the place correfponding with the fmall external the internal me- 



reaangle remained dry. l * h > produced 



° J drynefs on the 



8. If upon the • fmall external reclangle a difc of glafs be oppof. metal. 



applied, a round wet fpot is formed within in the middle f^ Jmall external 



the dry place of which we have juft fpoken, correfponding to middle of the 



the place occupied externally by the glafs. external metal, 



U 2 9. If 



produced wetuas 

 within, 



