428 Proceedings of Royal Society of Edinburgh, [july 18, 
12. An Experimental Critique of the Chloroplatinate 
Methods for the Determination of Potassium, including 
a redetermination of the Constant Pt. By Professor 
Dittmar and Mr John M‘ Arthur. 
13. Addition to Thermometer Screens. Part IV. By 
J. Aitken, Esq. 
{Added August 1887.) 
I much regret it has not been possible for me, during this 
summer, experimentally to determine the best forms and sizes of 
the details in the construction of the C screen ; nor have I been 
able to keep a continuous record of its readings. Only a few 
observations have been made at intervals with it, as originally 
constructed, and shown in fig. 1 of this paper, and with the 
Stevenson screens. The result of all these trials is to confirm the 
conclusions already arrived at. The C screen always gave the lowest 
readings when there was any radiation. The Stevenson screen, 
when worked under the ordinary conditions, that is with bottom 
open, generally gave on fine days readings of about two degrees too 
high; while the readings given with the Stevenson screen with 
bottom closed were higher than those of the C screen, but con- 
Date. 
Temp, by 
C Screen. 
Error of 
Stevenson 
Screen. 
Radiation 
by Large 
Ball. 
Radiation 
by 
Vacuum 
Thermo- 
meter. 
Temp, of 
Ball. 
Ratio x 
Temp, of 
Black Ball. 
Force of 
Wind. 
Temp, in 
Vacuum. 
July 23 
63°-9 
0°-6 
20° 
45° 
•44 
9 
3 
24 
65° 
l°-0 
28° 
69° 
•40 
11 
4 
25 
63° 
i°-o 
26° 
60° 
•43 
11 
4 
26 
69°T 
0°-9 
25° 
53° 
*47 
12 
3 
27 
67° -4 
0 o, 6 
22° 
41° 
•53 
12 
5 
28 
67° I 
0° -4 
23° 
49° 
•47 
11 
5 
29 
64° -4 
0°-6 
21° 
48° -5 
•43 
9 
4 
30 
63°-l 
l°-6 
29° 
62° 
•47 
14 
2 
31 
6 1°-5 
2° -3 
38° 
57° -5 
•66 
25 
1 
Aug. 1 
65° *9 
l°-6 
28° 
57° 
•49 
14 
2 
16 
66°‘9 
2°T 
28° 
44° 
•64 
18 
0-5 
17 
65°75 
1°*75 
29° 
51° 
•57 
16 
1 
18 
61° 
2° -6 
42° -5 
67°’5 
•63 
27 
0-5 
19 
62° -5 
2°-l 
38° 
66° 
•57 
22 
1 
