164 hertz's kesearches on electrical waves. 



Experiments iciththe secondary circuit in a horizontal plane. — The re- 

 sults obtained wlieu the plane of the secondary was horizontal can best 

 be explained by reference to the upper half of the diagiani in Fig, 8, 



In the position I, with the center of the circle in the line A A' pro- 

 duced, the sparks disappeared when the air space occupied either of the 

 hi or h'l, while two equal maxima of the sparking distance were obtained 

 at tti and a'l, the length of the spark in these positions being 2.5 milli- 

 meters. Both these results are in accordance with theory. 



In position JJthe circle is cut by the electromagnetic lines of force, 

 and therefore a does not vanish. It will however be small, and we 

 should expect that the expression a+/i sin 6* would have two unequal 

 maxima p-\-a and /i— a, both for ^=90°, and having the line joining 

 them perpendicular to the resultant E. m. f., and between these two 

 maxima we should expect two points of no sparking near to the smaller 

 maximum. This was confirmed by the observations. 



The maximum sparking distances were 3.5 millimeters at Uz and 2 

 millimeters at a'-z. Now with the air space at a2,^the sphere A being 

 l)ositive, — the resultant e. m. f. in the opposite portion of the circle will 

 repel positive electricity from A, and therefore tend to make it flow 

 round the circle clockwise. Between the two spheres the electrostatic 

 E. M. F. acts from A towards A', and the opposite e. m. f. of induction 

 in the neighborhood of the i^rimary acts from A' to A, parallel to 

 to the former, and acting more strongly on the nearer than on the 

 further portion of the secondary, tends to cause a current in the 

 same direction as that due to the former, namely, in a clockwise direc- 

 tion. Thus the resultant e. m. f. is the sum of the two as required 

 by theory, and in the same way it is easily seen that when the air space 

 is at a'2, the resultant e. m. f. is equal to their difference. 



As the position III is gradually approached, the maximum disap- 

 pears, and the single maximum sparking distance ^3 was found to be 4 

 millimeters in length, having opposite to it a point of disappearance a'3. 

 In this case clearly «=//, and the sparking distance is given by the 

 expression a (l-fsin H). The line a-itt'^j is again ijerpeudicuiar to the 

 resultant e. m. f. 



As the circle approaches further towards the center of A A', a will be- 

 come greater than /i, and the expression a-{-p sin B will not vanish 

 for any value of 0, but will have a maximum a-{-/3 and a minimum 

 a—fi, and in the experiments it was found thatthe sparks never entirely 

 disapi)eared, but varied between a maximum and a minimum, as indi- 

 cated by theory. 



In the position JV a maximum sparking distance of 5.5 millimeters 

 was observed at ^4 and a minimum of 1.5 millimeter at a'^. 



In the position Vthere was a maximum sparking distance of 6 millim- 

 eters at 0,5 and a minimum of 2.5 millimeters at a'5. In these experi- 

 ments the air space should ))e screened off from the primary in the 

 latter positions as well as in the earlier ones, in which it is unavoidable, 

 as otherwise the results would not be comparable. 



