12 BULLETIN OP THE LABORATORIES 



No change has been attributed to a change of the distance be- 

 tween primary and secondary plates by other experimenters, so far as 

 I am aware ; but a comparison of several of my curves seems to indi- 

 cate quite clearly that diminishing this distance increases the complex- 

 ity of the curve. 



It is worth noting that in each of these two and three following 

 careful determinations, the internodal space nearest the secondary 

 plates was about 5 mm longer than the other. This also has not been 

 elsewhere noted, so far as I know. 



As it was my plan to estimate the refractive index of a number of 

 liquids by surrounding a portion of two parallel stretched wires by the 

 liquid under investigation, it seemed desirable to use the wires much 

 nearer together than other experimenters or I myself had done before, in 

 order to avoid the necessity of using a larger amount of liquid than I 

 could readily obtain. I accordingly set up my apparatus again, with 

 the wires only three cm apart. By this change two distinct results were 

 produced. In the first place, the deflections produced corresponding 

 to the maxima positions on the wire were considerably reduced in 

 amount, viz : to about one third of the value before obtained. This 

 was easily provided for. As the galvanometer used had been adjusted 

 to only moderate sensitiveness, a new adjustment of it gave deflections 

 sufficiently large. The other change noticed by bringing the wires 

 nearer was a shortening of the interval between nodal positions. To 

 make sure of this result and to measure the amount of the change, 

 three complete determinations of the three maxima were made, read- 

 ings being made at each centimetre on the wire near the maxima posi- 

 tions. The results are as follows : 



The three determinations agree so well that there can be little 

 doubt of a shortening of the internodal interval by about 3 cni or 1.5 

 per cent. But the true change is more than this, for the bridges them- 

 selves form a part of the resonance system, and two-thirds of their 

 length should be added to the apparent internodal distance to get the 

 true half wave-length. The bridges were 12 cm long in the first in- 

 stance, and 3 in the second. This correction gave 17 1.2 as the half 



