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ZTbe jfoniiation of 2)ew* 



^T^HE following observations by Dr. J. G. McPherson, F.R.S.E., 

 ± Lecturer on Meteorology in the University of St. Andrew's, 

 are cited from the Wakefield Express : — 



" Until very recently the exact constitution of the nature and 

 formation of dew was unknown even by scientific men. The 

 opinion was generally held that if you sped through the glistening 

 meadow on a summer evening, through the diamond drops spark- 

 ling in millions, you would get your boots or trousers moistened 

 with dew. It was also believed that dew fell from the air upon the 

 ground. Now in both cases the opinion is wrong, for it is not 

 dew at all which was encountered in the meadow, and dew does 

 not fall from the air. If you look into the garden on a dewy 

 night — for there is such a thing as dew for all that — you will find 

 some plants moist. Glistening drops appear on the broccoli, but 

 the peas are dry. Place a hand-lantern below one of the healthiest 

 broccoli leaves, and you will find that the moisture is collected in 

 clear drops along the edge of the leaf and at the end of the veins 

 of the leaf The leaf veins radiating from the centre line of the 

 surface have carried the moisture of the healthy plant to the edges 

 to keep up plant circulation ; and the drops you see are not dew- 

 drops, but the watery juices carried out by the energy of the 

 healthy plant. For, place the lantern under an unhealthy leaf and 

 you will find no drops; there is no circulating vitality in it. Again, 

 examine grass blades, and you will find large drops near the tips of 

 the blades, the rest of the blades being quite dry. The large 

 drops seen on plants at night are falsely called dew ; they are pro- 

 duced from the plants themselves as tokens of their active and 

 healthy growth. 



This can be demonstrated in more than one way. Remove a 

 branch of poppy, and connect it by means of an indiarubber tube 

 with a head of water of about forty inches. After placing a glass 

 receiver over it to prevent evaporation, leave it for three hours. 

 Then you will find water has been freely excreted through the 

 veins, resembling what were familiarly called ' dew-drops.' If the 

 water pressed into the leaf is coloured with aniline blue, the drops 

 when they first appear are colourless, but before they grow to any 



