102 



RESEARCHES ON FUNGI 



Kleinii. it is necessary to take into account the laws relating to the 

 reflection of light at the surface of a transparent medium. When 

 a ray of light strikes the surface of a transparent medium such as 

 water, glass, or the cell-wall bounding the subsporangial swelling 

 of Pilobolus, part of it is reflected from the medium and part of 

 it is refracted into the medium. The percentage of light reflected 

 varies with the refractive index from air into the medium and with 

 the angle of incidence. The higher the refractive index, the greater 

 the percentage of light reflected. Also the greater the angle of 

 incidence, the greater the percentage of light reflected. The 

 percentage of light reflected for various angles of incidence at the 

 surface of a transparent medium when the refractive index from 

 air into the medium is 1* 55 is given in Table I.^ 



Table I 



Light reflected at the Surface of a Transparent Medium when the 

 Index of Refraction is 1 • 55 



1 F. E. Fowle, Smithsonian Physical Tables, Ed. 5, 1910, Washington, p. 191. 

 In tlie original Table the percentage of light reflected is set down as -^ (A + B). 

 According to Fresnel the amount of light reflected at the surface of a transparent 



sin ^ {i — r) , tan ^ (i — r) ' 



medium = ^ (A + B) 



sin 



-U 



{i + r) tan ^ {i + r) \ 



where A is the amount of 



light polarised in the plane of incidence, B that polarised perpendicular to this, 

 i the angle of incidence, and r the angle of refraction. 



