236 



Profs. W. E. Ayrton and John Perry. [Mar. 21, 





Temperature. 



1 TT 



1 -1 J2il 



t -hj 3 



X 



111 lllCg llUillfe. 



u 



8d Kj. 



A .1 A KO 



1052 



. KAAQ . , "I AG 

 5008 X 10" 



a 



OA° 



80 



A -T A At; 

 1005 



• KO A O ^ ~\ AS 



o24d X 10 



b 



77 4 



A -AOQ i 



uyo4 



. KOKK v/ 1 A6 

 OOOO X 10° 



c 



7b 5 



oyb4 



54bb X 10 



d 



70 / 



U O7o2 



•>71 QI7 1 A6 



/ iy / x iu° 



e 



70 6 



obyo 



7b0o X 10 



r> 

 I 



70 2 



A -A^700 



072o 



7288 x 10 b 



S 



(7AO .A 



/0 



A .A^7A1 



0701 



• •7 KT £? w T AG 



751b X 10" 



h 



,.ao . c; 



69 5 



ooyd 



• l7£?AO \/ 1 A6 



YbOo X 10 



i 



bb 8 



0b7b . 



77J4 X 10 b 



3 



b4 4 



A -f\A A O 



0442 



T -1 OO w 1 A6 



1 iy2 x 10 



k 



bz 8 



A -A/1 A£ 



040b 



1 zy8 x 10 



I 



£1 .a 



bi y 



A .AQQ1 



U O08I 



1 .QQQ w 1 A6 



± 080 X 10 



m 



b0 b 



A .AO/I K 



U 0o4o 



1 02/ X 10 



n 



5y o 



A .AOO K 



Oooo 



1 O/o X 10 



o 



57 5 



A .AOAA 



ozyo 



1 >Q1 i7 w 1 A6 



1 81/ X 10 



P 



5b 4 



A .AO £ O 



0252 



O -AAA ^ 1 AG 



2 oyo x 10 



q 



55 1 



A .Am A 



02iy 



O . A A£? >/ 1T6 



2 40b X 10° 



r 



COO . A 



53 4 



A .Al OA 



0180 



O -AO *7 ~\ A6 



2 y27 X 10 





too .a 



52 



A . Al K C 



015b 



O .0^70 v/ ~i A6 



o78 X 10 



t 



KAO .T 



50 1 



A .AT OT 



Old! 



A .AOO w 1 A6 



4 022 X 10 



u 



48° "4 



0112 



A .17 A /I v , 1 Afi 



4 704 X 10" 



V 



47° -0 



'0101 



5-217 xlO 6 



w 



45° -5 



-0075 



7-025 xlO 6 



p 



44° -0 



-0059 



8-930 xlO 6 



If we may assume that from P downwards in temperature the re- 

 sistance of gutta-percha follows the well-known logarithmic law, we 

 find at 24° C. the specific resistance per cubic centimetre is 83 X 10 6 

 megohms, showing that for a sheet the gutta-percha is fairly good. 



Ebonite, 



In determining the conductivity of ebonite, we at first proceeded as 

 dsscribed above, using a pair of copper plates ; but we found that the 

 charge instead of decreasing through conductivity increased apparently 

 indefinitely. On replacing the copper plates by sheets of platinum we 

 obtained consistent results, but this may have been due to the sulphur 

 that could easily be liberated by heat having been driven out in the 

 previous heating. QR is the curve connecting the conductivity, or 

 1 E 



rather - log — and the temperature. This curve is nearly straight 

 t E 2 



from 65° C. to 96° C, our highest temperature. No rapid change in 

 the conductivity is anywhere perceptible. 



As we could not employ the auxiliary condenser in consequence of 



