faARiJS -1 VISCOSITY OF GASES. 283 
Table 92.— Temperatures measured thermo-electrically and by the transpiration pyrometer. 
Aii- 
Air . 
Air 
Air 
520 
562 
567 
586 
598 
994 
996 
1212 
1217 
1219 
430 
436 
446 
455 
563 
568 
570 
575 
975 
981 
990 
1209 
1210 
1210 
[B"\ 
511 
549 
558 
572 
583 
964 
963 
966 
1217 
1227 
1222 
442 
450 
458 
467 
571 
574 
577 
580 
965 
971 
981 
1245 
1245 
1247 
Diff. 
+13 
+ 9 
+14 
+15 
+30 
+ 31 
+30 
- 5 
-10 
- 3 
-12 
-14 
-14 
-12 
- 7 
— 5 
+ 10 
+10 
+ 9 
-36 
-35 
-37 
6" 
L««] 
Diff. 
Hydrogen. 
958 
956 
+ 2 
960 
958 
+ 2 
962 
959 
+ 3 
962 
960 
+ 2 
970 
975 
- 5 
Hydrogen . 
1209 
1329 
-120' 
1212 
1338 
-126 
1215 
1337 
—122 
Hydrogen . 
414 
434 
- 20 
416 
437 
- 21 
421 
441 
- 20 
423 
445 
- 22 
Hydrogen 
507 
529 
- 22 
513 
535 
i 22 
515 
530 
- 21 
518 
541 
- 23 
520 
543 
- 23 
521 
543 
- 22 
Hydrogen. 
946 
963 
- 17 
952 
968 
- 16 
954 
974 
- 20 
955 
976 
- 21 
* Platinum pervious to hydrogen. 
The errors of this table are apparently large in places ; but they are 
by no means excessive when the great difficulties of experiment are 
justly taken into account. The observation of especial importance here 
is that the distribution of errors is promiscuous. A difference of 125° 
occurs in the case of hydrogen transpiring at 1,200°; but at this tem- 
perature platinum is seriously pervious to hydrogen. In some measure 
the errors are due to the fact that the gases referred to the same ?/ 
were not absolutely identical in composition. This is particularly the 
case in the final data for hydrogen in which the nearly constant error 
—20° is due to the erroneously low r/ here inserted — as I have already 
pointed out, page 271. Beyond this I believe that the differences of 
temperature remaining indicate actual differences of thermal environ- 
ment for the two thermometers here compared. They show that 
throughout the space enveloping the two pyrometers temperature was 
not rigorously constant, and it is quite in keeping with the present 
method of experiment to suppose that the mean temperature, 0", of three 
points as given by the thermo element, and the mean temperature [0"], 
for the length of nearly 67 cm of platinum capillary tube, will not even in 
(937) 
