120 Profs. W. E. Ayrton and J. Perry on 



distances measured from the line to the curve ABODE 

 representing conductivityj the specific resistance per cubic 

 centmietre at B, for instance, being 2240 megohms. F G is 

 a continuation from E one tenth as great for vertical distances 

 (that isj for conductivity), but on the same scale for horizontal 

 distances. Again H 1 is a continuation from G on a scale 

 one hundredth as great for vertical distances as in the curve 

 ABODE, and JK on a scale for vertical distances one 

 thousandth as great, the scales for horizontal distances in all 

 the curves being the same. The curve L M ]N" P Q is drawn 

 so that vertical distances measured from the line X X repre- 

 sent temperature, and horizontal distances time — the zero for 

 time, and the length corresponding with one minute, being the 

 same as for all the other curves ; negative temperature is re- 

 presented upwards and positive temperature downwards — the 

 point L corresponding with a temperature of — 13°*1 0. 



The current continued to diminish regularly to the point B, 

 when the temperature shown by the point M was — 12°*3 0., 

 and the time 10 minutes past 3. At this point and at the 

 other steep places in the curves, water w^as thrown into the 

 freezing-mixture to raise its temperature ; and at such points 

 as 0, where the current had evidently reached a maximum at 

 a corresponding temperature IST, the readings are supposed to 

 represent the true conductivities at the corresponding tempe- 

 ratures; but this, of course, is only approximately accurate. 

 It is very striking how the maxima of conductivity and tem- 

 perature correspond with one another, considering that the 

 thermometer only indicated the temperature of the air in the 

 copper box above the ice, whereas change of current indicates 

 change of state in the ice itself. The very great increase in 

 conductivity which occurs at the melting-point is seen to be 

 quite regular, and unlike what one might expect from the dis- 

 continuity of the solid and liquid states. 



Taking the corresponding conductivities and temperatures 

 at points 0, N, &c., we have drawn the curves II S, TV 

 (fig. 3). Horizontal distances to the right of YY represent 

 positive temperatures, and to the left negative, on such a scale 

 that the point R corresponds with a temperature of — 12°-4 0. 

 Vertical distances measured from X X represent conductivity 

 on such a scale that the point P corresponds with a i^esistance 

 per cubic centimetre of 2240 megohms. T V is a continuation 

 from S on a scale for vertical distances three thousandths of 

 that employed in the curve R S, the scale for temperature re- 

 maining as before: the point V thus corresponds with a resist- 

 ance per cubic centimetre of 0*33 megohm at a temperature 

 ll°-02 0. From the curves (fig. 3) it would appear that the 



