110 OF EVAPORATION. CHAP. 2. 21. 



other, and looking at a Halo, see the same 

 light: but as the Halo is seen for a great 

 extent around by persons in different places, 

 a disposition to such reflexion or refraction of 

 the rays is inferred as existing in large and 

 extensive masses of the same cloud. It may be 

 a fit subject of inquiry, At what distances is 

 Halo seen at the same time ? Sometimes the 

 cloud seems very partial, but at others very 

 extensive. When a Halo appears in a cloud, the 

 extremities of which can be seen, it may serve 

 to mark that cloud as a subject of geometrical 

 observation at several distant stations, whereby 

 its distance and magnitude may be nearly 

 ascertained. 



In some parts of America, Halos are said to 

 be still more common than in England. 



SECTION XXI. 



Of the Evaporation of Water. 



ACCORDING to the most recent theory, the 

 following will be the process of evaporation. 

 The accession of diurnal temperature commu- 

 nicating to the water the power of calorific 



