62 



PRESSURE OF LIGHT 



Observed torque in 

 icr 6 cm. dynes. 



Calculated torque in 

 io~ 6 cm. dynes. 



2 7'6 7'i 



3 4'6 3'0 



4 8-8 5-3 



The effect of shifting a beam parallel to itself 

 was tested by another experiment. A rectangular 



'A 



FIG. 28. 



block of glass 3 cm. x I cm. x I cm. was sus- 

 pended in the exhausted case with its long axis 

 horizontal, and a beam of light was passed through 

 it in a horizontal plane, as shown in fig. 28 plan, 

 the beam emerging along EF parallel to its line of 

 incidence AB. 



Again the block was turned round in the 

 direction of the circular arrow, but as the fibre 

 was rather coarse the deflexion was very minute. 

 To render the effect more evident the beam was 



