12 



Page. 

 Chapter V. The Methods of Measuring Direct or Diffuse Sunshine 



AS to Intensity or Duration . 81 



Theoretical relation of direct and diffused sunshine (Clausius) 81 



Total insolation, direct and diffused (Marie-Davy) , ^ ^ . . 82 



Theoretical formulae for actinometer (Arago-Davy: Marie- Davy: Fer- 



rel) 87 



Intensity and duration of sunshine at Montsouris (Marie-Davy) 89 

 Relative total heat received from sun and sky diiring any day by hori- 

 zontal surfaces ( Aymonnet) 90 



^-~ilelative total heat received during certain months (Aymonnet) 92 



Photo-chemical intensity of sunshine (Bunsen: Roscoe) . 92 



Photographic intensity of sunshine ( Vogel: Weber) 95 



Marchand's self-registering chemical actinometer 96 



Comparison of Marchands and Marie- Davy's results (Radau) 96 



Violle's conjugate bulbs 97 



Bellani"s radiometer or vaporization actinometer (Descroix) 97 



Arago"s cyanometer and Desain's thermo-electric actinometer -99 



Duration of sunshine — 



Recorded at United States Signal Service stations 99 



Recorded at Winnipeg, Manitoba . - . . 100 



Total possible duration of sunshine, by decades (Schott; Libbey) 101 



Chapter VI. Moisture of the Soil 104 



In general ... 104 



Evaporatio.. from the surface of fresh water in evaporometer (Descroix; 



^^-_^ ?erald; Piche; Riissell) 104 



Culti \ ation diminishes surface-soil evaporation (Sturtevant) 108 



Percol.^tion ( Welitschkowsky; Whitney; Goff ) 100 



Available moisture ( Wollny; Haberlandt: Seignette) 110 



Transpiration (Hoehner: Wollny; Risler; Marie-Davy: Perret) 112 



Relation of plants to moisture of soil ( Wollny) . 114 



Relation of water to crops (Ilionkoff: Haberlandt; Hellriegel; Fitt- 



bogen; Birner; Heinrich; Wollny; Sorauer) ^.. 116 



Rainfall and sugar beets (Briem; Grassmann) 125 



Chapter VII. Miscellaneous Relations 128 



Rapid thaws , , 128 



Wind :. 129 



The organic dust of the atmosphere (Serafina; Arata) 130 



Atmospheric electricity ( Wisliczenus; Marie-Davy) 131 



Chapter VIII. Relation of Plants to Atmospheric Nitrogen 133 



In general 133 



"The amount of nitrogen brought down by the rain to the soil (Marie- 

 Davy: Muntz: Marcano) 133 



Nitrogen directly absorbed by soil (Schloesing) 136 



Fixation of nitrogen by plants (Hellriegel and Wilfarth; Breal; Lawes 

 and Gilbert; Frank; Berthelot; Heraeus; Warini;ton; Maquenne; 



Wheeler; Leone; Woods; Petermann; Pagnoul; Salkowsky) 136 



Chapter IX. Relations of Crops to Manures and Fertilizers, and 



Rotation 162 



Artificial fertilizers and manures (Sanborn; Ohio; Ladd; Prize crops 



of 1889) 162 



