684 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



3. Experiments to show a Possible Effect of the Surfaces of a Screen 



on Transmission. 



Experiments "with two metals, aluminium and copper, were made in 

 order to find evidence of any effect which the surfaces of the screen 

 might exert on transmission. The results in both cases were negative. 

 These experiments were conducted in the following way : 



A set of screens of different thicknesses was prepared, each screen 

 consisting of a single solid piece of the metal in question. A second 



.01 .02 .03 .04 .06 06 .07 .08 09 .10 .U 02 .13 .04 .16 .16 



THICKNESS CM. 



Figure 5. 



This figure shows the small effect of the surfaces of screens upon transmission, 

 in the case of aluminium and of copper. Tlie curves are obtained by plotting 

 as abscissa the thickness of each of a set of one-piece screens of the metal under 

 examination against tlie corresponding "relative deflection" (that is, the deflec- 

 tion observed wlien the screen is interposed divided by the deflection observed 

 when the screen is withdrawn) as ordinate. The crosses are points on a curve 

 obtained when laminated screens were substituted for one-piece screens. 



set of screens was made, similar to the first except that the screens 

 were laminated. The pieces of metal used were brightly polished on 

 both sides. From the first set of screens a curve was obtained by the 

 method described on page 6S1. A similar curve was taken for the 

 laminated screens, and lastly, to check the constancy of the tube, a 

 second curve for the solid screens. Readings were taken at intervals 

 of one minute, and in these experiments the rays were not allowed to 

 run until the greatest attainable deflection occurred, but were cut off 



