g8 Mr. Baldwin Latham. 



Observations made by Professor John Phillips, F.R.S., in 

 1843-4, showed the following results : — 



Height above ground. Rainfall. 



Inches. 



14 feet 26-559 



3 >> 26*298 



6 ,, ... ... ... ... 26"i89 



12 ,, 26039 



24 .. 24-158 



Observations were also made by Mr. R. Crimes, at the 

 Rotherham Water Works, the Rev. T. E. Crallan, the Rev, 

 F. W. Stow and others, the results of which are recorded in 

 Mr. Symons' " British Rainfall," and all show that there is 

 certainly less rain collected by the rain gauge as we ascend 

 from the ground. 



A number of theories have been advanced as to the cause of 

 this apparent diminution of rain with elevation. The most 

 popular was that of Benjamin Franklin, that it was due to the 

 condensation of the falling rain drops as they descend through 

 the air, the rain drop descending from a considerable altitude 

 condensed the vapour in the lower regions up it. Calcula- 

 tions, however, were made by Mr. James Glaisher, F.R.S., 

 some years ago, which show that if all the vapour in the air 

 were to condense, it would add but an infinitessimal increase 

 to the rain drop in the last few hundred feet of descent, and 

 nothing like the amount of the increase observed as we descend 

 from the higher to the lower regions of the atmosphere. 



Another cause has been ascribed to the difference in the 

 electrical tension of the rain drop above the ground, the 

 electrical attraction increasing as the rain approaches the 

 ground, thus causing it to increase in bulk. 



M. Arago showed that rain drops do increase in size, and 

 become irregular in shape as they approach the surface of the 

 ground, as signified by the disappearance of the supernumerary 

 rainbow, but in all probability this phenomena is due to the 

 drops becoming irregular in size from cohesion. 



The cause of this apparent diminution of rainfall with 

 altitude is more fictitious than real, and is due to the mode in 

 which rainfall is collected. The cause was shown by Professor 

 Phillips, F.R.S., some years ago to be due to the varying 

 angle at which rain falls. From experiments made by Pro- 

 fessor Phillips with a globular gauge, he was able to collect 

 more rainfall with an increase of altitude above the ground 

 line, as will be seen from the following figures : — 



Ground line. 3-ft. above. 6-ft. above. 12-ft. above. 

 2-905 2-957 2-934 3"ii5 



In this case as the angle at which rain falls becomes less 



