TABLE 251. 



DIELECTRIC STRENGTH. 



Difference of Electric Potential required to produce a Spark in Air. 



(a) MEDIUM, AIR. ELECTRODE TERMINALS, FLAT PLATES. 



Spark length 



in 

 centimetres. 



O.O[ 

 0.02 

 O.O4 

 O.O7 

 O.IO 

 O.I4 

 O.2O 

 0.30 

 O.4O 

 0.50 

 0.60 

 0.80 

 I.OO 



Difference of potential in volts required to produce a spark according to 



W. Thomson. 1 De la Rue. 2 MacFarlane. 3 Bailie. 4 Freyberg. 5 



79 

 1340 

 1840 

 2940 

 4010 



53 



500 

 970 

 1900 



4330 



5740 



762.0 



10400 



35_7 



5715 



7818 



9879 



11925 



13956 

 18006 



4401 



7653 

 10603 



I 343 I 

 16341 

 19146 

 2S45 8 

 3*647 



4344 



7539 

 10671 

 13665 

 16293 



19059 

 24465 

 28800 



1 " Reprint of Papers on Elect, and Mag." p. 252. - " Proc. R. Soc." vol. 36, p. 151. 



3 " Phil. Mag." vol. 10, 1880. 4 " Ann. de Chim. etde Phys." vol. 25, 1882. 



5 " Wied. Ann." vol. 38, 1889. 



(b) MEDIUM, AIR. ELECTRODE TERMINALS, BALLS OF DIAMETER d IN CENTIMETRES. 



Experiments of Freyberg. 



Spark length 



in 

 centimetres. 



d = o (points). 



= 6.o 



O.I 

 0.2 



0-3 

 0-4 

 0.6 



0.8 



I.O 

 2.O 



3720 

 4700 

 5300 



6000 

 6900 

 8100 



8600 



IOIOO 



13100 



5050 

 8600 



18400 

 19500 

 24600 



30700 



4660 



9500 



11700 

 14000 



19300 

 23200 



25800 



35400 



4560 



8700 

 11600 

 14400 

 19500 

 24600 

 29000 



8400 



II200 



14200 



2CTOO 

 25800 

 29900 



4530 



7900 



10500 



I92OO 

 26OOO 

 3I6CO 



From the above table it appears, as remarked by Freyberg, that for each length of spark there is a par- 

 ticular size of ball which requires the greatest difference of potential to produce the spark. 



(c) COMPARISON OF RESULTS OF DETERMINATIONS, THE TERMINALS BEING BALLS. 



Spark 

 length 

 in cms. 



Difference of potential required to produce a spark in air according to 



Bailie. 



Bichat and 

 Blondlot.' 



Balls i centimetre diameter. 



Paschen. Freyberg. Quincke. 2 



Balls 2 cms. diameter. 



Bailie. Freyberg. 



Balls 6 cms. diam. 



9 

 r.o 



4590 

 8040 

 11190 

 13650 

 16410 

 19560 

 21690 

 23280 

 24030 

 24930 



4200 



8130 



10860 



14130 



16800 



19350 

 21030 

 23190 

 24540 

 25800 



4860 

 8430 

 11670 

 14830 

 17760 

 20460 

 22640 

 24780 



4660 

 9500 

 11670 

 13980 

 16800 

 19260 

 20970 

 23220 

 25110 

 25770 



4830 

 8340 

 11670 

 14820 

 18030 

 20820 

 23670 



4560 

 8700 

 "550 

 14400 

 17040 

 19470 

 22530 

 24630 

 27240 

 29040 



4440 

 7920 

 11190 

 14010 

 16920 

 19980 

 22590 

 25770 



4440 



7680 



10830 



1350 

 16530 

 19560 

 22620 

 26400 

 29220 

 33870 



4530 

 7860 

 10470 

 12750 

 16410 

 19200 

 22590 

 26010 

 28770 

 31620 



1 " Electricien," Aug. 1886. 



2 " Wicd. Ann." vol. 19, 1883. 



SMITHSONIAN TABLES. 



244 



