ELECTRIC DISCHARGES IN GASES AT LOW PRESSURES. 
411 
error in reading the potential diderence would result in a large error in the pressure 
readings. It is interesting to note, however, that even under these unfavourable 
conditions a striking agreement is presented between the results obtained at critical 
pressures and the results demanded by Paschen’s law. 
In order to make the agreement between the numbers demanded by Paschen’s law 
and those obtained in these experiments still more evident, the results recorded in 
Table I. are again given in a slightly different form in Table II., where each potential 
difference is associated with the product of the pressure at which discharge took place 
and the corresponding spark length. Paschen* found that at high pressures these 
products were constant for different distances between the electrodes, as long as the 
applied potential difference was the same. 
The numbers recorded in Table II. show that the same law is rigidly applicable to 
all pressures, both high and low. 
Table II.—Air. 
Spark length 
= 1 millim. 
Spark length 
= 2 milliins. 
, Spark length 
= 3 millims. 
Spark length 
= 5 millims. 
Spark length 
1 =10 millims. 
! 
Product 
of 
pressure 
and spark 
length. 
Spark 
potential 
in 
volts. 
Product 
of 
pressure 
and spark 
length. 
Spark 
potential 
in 
volts. 
Product 
of 
pressure 
and spark 
length. 
Spark 
potential 
in 
volts. 
Product 
of 
pressure 
and spark 
length. 
Spark 
potential 
in 
volts. 
Product 
of 
pressure 
and spark 
1 length. 
! 
Spark 
potential 
in 
volts. 
150 
1510 
40 
620 
153 
1480 
.36-7 
600 
70-9 
831 
120 
1265 
26-4 
527 
124-5 
1275 
23-0 
504 
41-2 
645 
90 
1025 
17-4 
455 
94-5 
1015 
14-7 
418 
23-9 
504 ! 
61 
784 
11-0 
400 
64-2 
790 
9-25 
368 
1.3-9 
420 
40-8 
634 
8-22 
373 
42-3 
630 
7-85 
356 
9-82 
.372 
21-6 
489 
6-.32 
355 
27-9 
526 
6-70 
349 
8-05 
355 
19-4 
477 
5-42 
351 
17-9 
452 
5-70 
352 
6-79 
348 
12-4 
417 
4-64 
357 
11-5 
405 
4-91 
359 
5 - 62 
.351 
7-77 
367 
4-04 
371 
7-53 
371 
4-19 
370 
4-66 
359 
6-66 
.357 
3 • 50 
389 
6-54 
361 
3-57 
.388 
.3-84 
377 
5-80 
352 
3-04 
419 
5-67 
356 
3-0.3 
427 
.3-12 
425 
4-98 
349 
2-60 
460 
4-92 
.358 
2-58 
484 
2-59 
.504 
4-27 
355 
2-26 
534 
4-26 
364 
2-20 
575 
2-19 
605 
3-67 
368 
1-96 
654 
3-66 
375 
1-87 
705 
1-80 
757 
3-15 
392 
1-71 
826 
3-18 
397 
1-60 
935 
1-52 
1020 
2-70 
429 
1-50 
1042 
2-78 
441 
1-38 
1223 
1-25 
1315 
2 • 35 
481 
1-28 
1312 
2-41 
494 
1-16 
1585 
1-05 
17.30 
2-02 
558 
1-09 
1695 
2-1.3 
576 
1-08 
1774 
_ 
_ I 
1-74 
681 
1 -07 
1829 
1-84 
691 
— 
— 
_ 
_ j 
1-51 
855 
— 
.- - 
1-60 
863 i 
— 
— 
_ 
_ j 
1-29 
1090 
— 
— 
1-39 
1092 
— 
_ 
_ 
1-12 
1463 
— 
— 
1-23 
1395 ! 
— 
— 
_ 1 
_ 
1 -05 
1826 
1 
— 
— 
1-07 
1786 
— 
— 
— 
— 
* Paschen, ‘Ann. d. Phys.,’ vol. 37, p. G9. 
3 G 2 
