562 PROCEEDINGS OP THE AMERICAN ACADEMY. 



the same state, as nearly as we could tell, in which the annealing had 

 left it. These details are mentioned for the reason that it was important 

 to test after the annealing the same points, as nearly as might be, which 

 had been tested before the annealing; for sometimes a movement of one 

 or two millimeters along the wire made a serious change in the effect 

 observed. 



After being annealed the wire was tested again, just as it had been 

 tested before. Curve C 2 of Figure 7 shows the result. This curve is 

 very different from C lt having a smaller number of changes of sign, 17 

 (or at most 19) instead of 22, and a greater vertical range, the greatest 

 electromotive force indicated by C 2 being aproximately 30 X 10 -s volt, 

 as against the 16 X 10~ 8 volt which is the maximum of Ci. 



The question arose whether the effects observed could be due in any 

 considerable measure to the surface condition of the wire. Accordingly 

 we now rubbed it with fine emery paper, thus removing at least a large 

 part of the black coating left by the annealing and making the surface 

 comparatively bright once more. After this treatment we tested the 

 wire again, just as before, with the result shown by C 3 . Comparison 

 of curves C 2 and C 3 shows them to be very much alike, the differences 

 of detail being, perhaps, no greater than might be expected from two 

 successive tests made without change of condition of the wire. 



The next question considered is whether the effects observed are duo 

 to slight local bends in the wire, such bends being rather difficult to 

 avoid. It is true that previous experiments, already described, made 

 with spiral wire in combination with straight seemed to give a negative 

 answer to this question, but it was easy and interesting to come at the 

 matter in another way. Accordingly, after marking the 25 cm., 50 cm., 

 and 75 cm. points of the wire with knots of thread, we stretched it 

 until the 50 cm. length which we had especially studied became per- 

 manently 55 cm. long, thus taking out any small bends which lay in 

 this part of the wire before the stretching. Then we readjusted the 

 wire on the rack in such a way as to bring opposite the 25 cm. mark 

 of the meter-rod the same point of the wire which had previously been 

 there and to bring opposite the 80 cm. mark of the rod the same point 

 of the wire which had previously been opposite the 75 cm. mark. 

 Then we made a test as before, touching the ice first at the 25 cm. 

 point, then at the 26.1 cm. point, then at the 27.2 cm. point, and so on, 

 by stages of 1.1 cm., to the 80 cm. point, thus trying to get at the 

 same points in the wire which had been used before the stretching. 

 It is to be noted, however, that a wire stretched through the whole of 



