THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES. ] 



Art. XXX Y. — Irregular Reflection ; by C. C. Hutchins. 



In photometric work it has been customary to assume the 

 validity of Lambert's fundamental law- of reflection ; namely, 

 the amount of light sent from one surface element f to 

 another surface element m is proportional to 



f. in. cos s cos v 



where r is the line joining the two elements, and s and v are 

 the angles made between /• and the normals to the two ele- 

 ments. The truth of this law seems to be borne out by com- 

 mon experience. Thus a sheet of paper illuminated by 

 perpendicular rays, — the globe of a student lamp, seems equally 

 illuminated at all points of view, and other examples of a simi- 

 lar nature will readily suggest themselves. 



This seeming agreement of fact with theory, however, does 

 not do away with the desirability of an experimental investiga- 

 tion of the subject. 



The matter has been dealt with for certain bodies, for 

 instance the moon, photometrically by Zollner and others, and 

 its total radiant energy with respect to phase has been measured 

 by Ross and Very ; but the measurement in the laboratory of 

 the total reflection of bodies at different angles of reflection is, 

 as far as can be learned, new. 



Suppose a plane surface of small dimensions illuminated by 

 perpendicular rays and seen at a fixed distance at different 

 angles ; then the effect produced at the point of view will be 

 proportioned to the cosine of the angle of reflection, provided 

 the plane surface is without specular reflection. 



Am. Jour. Sci. — Fourth Series, Yol. VI, No. 35. — November, 1898. 

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