756 
PROFESSOR O. REYNOLDS ON CERTAIN DIMENSIONAL 
Table XIII.—Thermal transpiration of hydrogen by stucco plate No. 2 (“25 inch or 
6’35 millims. thick). Temperature of steam, 212° F. or 100° C.; temperature of 
water, 70° F. or 21° C. 
Mean pressure by vacuum 
Difference of pressure by siphon gauge. 
Ratio of 
mean pressure to 
Log of mean 
Log of 
difference of 
pressure. 
gauge. ‘ 
July 19. 
July 20. 
difference of 
pressure. 
pressure. 
inches. 
31-00 
millims. 
787-40 
inc v . 
inch. 
•1072 
millims. 
2-723 
290 
2-491-1 
2-030-3 
30-55 
775-50 
•1080 
2-743 
283 
2-484 
2-033 
29-60 
751-60 
•1084 
2-753 
273 
2'456 
2-035 
28-10 
713-70 
•1102 
2-799 
255 
2-449 
2-042 
26-70 
677-90 
•1122 
2-850 
237 
2-426 
2-050 
25-50 
647-50 
■1132 
2‘875 
225 
2-406 
2-054 
25-25 
641-00 
•1130 
2-870 
223 
2-402 
2-053 
24-15 
613-40 
•1152 
2-916 
209 
2-383 
2-061 
22-40 
568-90 
•1180 
2-997 
190 
2-350 
2-072 
22-05 
560-00 
•1176 
2-977 
188 
2-343 
2-070 
21-10 
535-90 
•1182 
3-002 
177 
2-324 
2-072 
20-15 
510-50 
•1186 
3-012 
170 
2-304 
2-074 
20-00 
508-00 
•1192 
3-027 
168 
2-301 
2-076 
19-20 
487-60 
•1190 
3-023 
160 
2-283 
2-075 
17-15 
435-60 
•1204 
3-058 
142 
2-234 
2-080 
16-20 
411-40 
•1208 
3-068 
134 
2-209 
2-082 
16-00 
406-40 
•1214 
3-083 
130 
2-204 
2-084 
15-30 
388 60 
•1214 
126 
2-185 
2-084 
14-60 
370-80 
•1220 
3-098 
119 
2-164 
2-086 
14-55 
369-50 
•1220 
5? 
2-163 
2-086 
13-95 
354-30 
•1220 
114 
2-144 
2-086 
13-20 
335-20 
•1212 
3-078 
108 
2-120 
2-083 
12-35 
317-70 
1216 
3-088 
101 
2-091 
2-085 
11-95 
281-80 
1200 
•1200 
3-048 
100 
2-077 
2-070 
10-70 
271-80 
•1198 
3-043 
89 
2-029 
2-087 
9-60 
243-80 
•1176 
2-987 
80 
1-982 
2-070 
8"65 
219-70 
•1146 
2 910 
75 
1-937 
2-059 
7-75 
196-80 
1120 
2-844 
69 
1-889 
2-049 
6-30 
160-00 
•1064 
2-702 
60 
1-799 
2-027 
5-75 
146-00 
TO'OO 
2-540 
56 
1-759 
2-000 
5-10 
129-50 
•0976 
2-479 
52 
1-700 
1-989 
3"65 
92-70 
•0854 
2-169 
42 
1-562 
1-931 
3-40 
86-30 
•0860 
2-184 
40 
1-531 
1-934 
2-50 
63-50 
•0704 
1-788 
35 
1-398 
1-847 
1-60 
4000 
•0524 
1-331 
30 
1-204 
1-719 
1-10 
27-90 
•0420 
1-066 
26 
1-041 
1-623 
•35 
8-88 
•0170 
•431 
20 
0-544 
1-230 
In making the experiments contained in Tables XII. and XIII., there was a slight 
change from the former plan, which had been to begin at the higher pressures and 
thence proceed by successive exhaustions to the lower pressures. This time one series 
of experiments was made as before, and another in the inverse manner—the diffusio 
meter being exhausted to commence with and the air or hydrogen being allowed to 
enter between the observations. Both series are given in the tables and are seen to 
agree very closely. 
In the case of hydrogen it was found as before, that although not great, there was 
