AXIAL AND OBLIQUE RADIATION. 



28 > 3. 33 > afl d 34 are deficient from the gradual loss of strength of the 

 X-ray bulb; but the data for s in the axial case are nevertheless larger 

 than for the cases where the rays grazed the top or the bottom of the 

 fog chamber. In the latter, the corona is particularly small and open 

 on top, showing the absence of nuclei in the upper strata of the air of 

 the fog chamber. Thus the endeavor to directly call out the nuclei 

 from the top or the bottom of the fog chamber has again failed. 



6 



FIG. 13. Fog chamber with axial and oblique radiation. 



,-u 

 A final test on the effect of the walls was made in a somewhat dif- 



ferent manner by placing the bulb at a distance of 80 cm. from the 

 chamber C, figure 13, at first axially, as shown at a, and then in the 

 raised position, b. In the first instance the rays pass through the 

 least surface of wood and the incidence within is grazing; in the second 

 (nonaxial), the rays pass through a much larger surface of wood and 

 the incidence is at a large angle. Table 9 shows the results in the two 

 cases to be identical, barring increased distance and the tendency of 

 the bulb to lose efficiency in the lapse of time. In the present case, 

 however, the nuclei are of the fleeting kind discussed in the chapters 

 below, and comparison with the above persistent nuclei is not at once 

 permissible. 



TABLE 9. Comparison of axial end oblique rays 



23.3 cm. 



'Periodicity. Difference due to X-ray bulb. fAir s = 1.5. J s% i.o. 



