36 Harvey on the Deposition of Dew. 



of the glass was sufficiently lowered, to adroit the stratum of air in 

 contact with it, to impart a portion of its moisture. The dew first 

 made its appearance on each of the vitreous surfaces, like the 

 effect produced by a gentle breathing. There was a difference, 

 however, in the manner in which the moisture was deposited on 

 the two glasses. In the crystal without the ferrule, it was confined 

 to a zone, bounded on one side by the edge cf the glass, and on 

 the other by the circumference of a dry transparent circular space, 

 formed in the middle of the surface, of an inch and quarter diame- 

 ter; but in the other, the circumference of the dry lucid circle 

 formed the inner boundary of the dewy zone ; and a circle distant 

 about a quarter of an inch from the circumference of the glass, 

 formed the outer. At half past nine, the particles on the inner 

 edges of both zones, preserved their minuteness ; but in the former 

 glass there was a small but perceptible increase in their magnitude, 

 to its extreme edge; whereas, in the other, the increase proceeded 

 not only from the inner edge, but from the outer, producing thereby 

 the largest particles in the middle of the zone. 



At the expiration of an hour, a new appearance was presented. 

 Within the dewy surface of the former crystal, another very nar- 

 row zone of moisture was perceptible, composed of exceedingly 

 fine particles. The two zones were not blended together, a dis- 

 tinct line of separation being visible between them. The formation 

 of the latter necessarily diminished the diameter of the lucid cir. 

 cle, since the whole of it appeared to have been formed within the 

 dry space. The surface of the glass, therefore, was divided into 

 three compartments : 



1st. The outer zone, composed of particles decreasing from its 

 exterior to its interior boundary. 



2d. The narrow zone of very fine particles, its greater circum- 

 ference being in contact wilh the inner boundary of the former. 



3d. The dry transparent circle. 



The surface of the other crystal presented a similar zone of mi- 

 nute particles, on each side of the first mentioned dewy zone ; so 

 that its surface was divided into five compartments : 



1st. A dry transparent zone. 



