OF DENISON UNIVERSITY. II 



the whole length of the wire. Many such series of observations were 

 made, the conditions being varied somewhat to learn the effect of such 

 variations. The results may be best presented in the form of curves, 

 abscissae representing positions of the bridge on the wire and ordinates 

 the corresponding galvanometer deflections in millimetres. 



Rubens had noted that the number of maxima in a curve is dimin- 

 ished by (a) increasing the distance between the primary plates, and 

 (d) leaving a bridge at a maximum position and exploring with a sec- 

 ond sHding bridge. 



These facts are shown repeatedly in my curves. Thus in curve 

 D (Plate I) there are six strong maxima and seven or eight weaker 

 ones. Abscissae represent position of the wire bridge as measured by 

 a tape measure divided to centimeters stretched between the parallel 

 wires, and ordinates the corresponding galvanometer deflection in mil- 

 limeters. In this experiment the primary plates were 4.5 cm. apart. 

 By increasing this distance to 8 cm. the three strong maxima (separated 

 from one another by intervals of 146 cm.) almost disappeared, the 

 other three remaining. 



Again, by leaving a bridge in the position corresponding to the 

 maximum nearest the secondary plates and exploring with a second 

 bridge, all but three of the 15 maxima practically disappeared. These 

 three occupied positions 8, 154.5 and 303.5 cm., at practically equal 

 distances apart and are shown in curve G. The maximum near the 

 middle of the wires was especially sharp, the two others weaker by the 

 same amount. The effect of a fixed bridge is thus to reduce a some- 

 what complicated wave system to a simple one. 



The maxima obtained were so improved in both strength and 

 sharpness by the use of a second bridge that two very careful determi- 

 nations of their position were made to get an idea of the degree of 

 precision allowed by this method of calculating the half wave-length. 



The results are as follows : 



The nodal positions seemed to be capable of being located to with- 

 in a fourth of a centimeter, and on repeating the experiment the same 

 results could be expected within a half centimeter. 



Still greater steadiness and definiteness were secured in some later 

 experiments by the use of three or even four fixed bridges. 



