24 
PROFESSORS W. E. AYRTON AND J. PERRY 
Date. 
The following — 
Has to the following— 
At— 
A contact 
difference 
of 
potentials, 
in volts. 
Remarks. 
°C. 
28/2/78 . 
Copper. 
Alum, saturated at 16 0- 5 C.. 
15 
-0-243 
Each of the numbers in the 
Zinc. 
)) 
17-8 
-0-536 
preceding column is the 
Lead. 
Sal-ammoniac, saturated at 
18 
-0-189 
average of about ten obser- 
17° C. 
vations. 
Iron. 
18 
-0-652 
Lead. 
1 of sulphuric acid, 5 of dis- 
17 
-0-120 
tilled water. 
3/3/78 . 
)) . 
Distilled water. 
17 
+ 0-167 
J» ^ . 
Iron. 
Alum, saturated at 16°'5 C.. 
16 
-0-139 
16 
-0-653 
4/3/78 . 
Lead. 
Distilled water . 
15-5 
+ 0-163 
Solution sea-salt, saturated 
17 
-0267 
at 17° C. 
Iron . 
18 
-0-605 
Zinc . 
15 4 
-0-624 
Copper . 
51 J> 
16 
-0-524 
5/3/78 . 
Lead . 
Alum, saturated at 16°'5 C.. 
16 
-0-139 
Iron. 
9 > 
Mercury . 
16 
-0-653 
6/3/78 . 
,, . 
19-4 
+ 0-501 
Copper . 
>» . 
Brass . 
19 
+ 0-378 
7/3/78 . 
„ . 
19 
-0-151 
Zinc . 
18 
+ 0-679 
Iron . 
19 
+ 0-064 
Lead . 
18-5 
+ 0-472 
Tin. 
.. 
18-5 
+ 0-372 
Platinum. 
.. 
18-6 
-0-287 
Solution sea-salt, saturated 
18 
-0-856 
at 17° C. 
Tin. 
17'8 
-0-304 
Sal-ammoniac, saturated at 
18 
-0-364 
15°*5 C. 
8/3/78 . 
Platinum . 
17 
+ 0-057 
„ . 
Alum, saturated at 16 0, 5 C. . 
17 
+ 0-246 
Tin . . . 
17 
-0-225 
9/3/78 . 
5) ' *. 
Distilled water . 
14-5 
+ 0-177 
Iron . 
Mercury . 
16 
+ 0 503 
Lead . 
» . 
15 
+ 1-00 
rapidly 
diminish- 
ing to 0 
11/3/78 . 
Tin . 
1 of distilled water, 5 of 
16 
-0-256 
sulphuric acid by weight. 
Brass . 
15 
+ 0-016 
Distilled water . 
14 
+ 0-207 
Solution sea-salt, saturated , 
14-5 
-0-435 
Alum, saturated .... 
14-5 
-0-014 
Sal-ammoniac, saturated. . 
14 
-0-335 
12/3/78 . 
Tin . . , . 
Distilled water. 
16 
+ 0-177 
Platinum. 
Mercury. 
17 
+ 0-204 
Here 
a number of apparently very discordant results were obtained when experimenting with mercury. The 
explanation at length was found to be due to the apparent contact difference of potentials between a metal and 
mercury as measured inductively, varying much with small alterations of temperature. 
How as the mercury was 
redistilled in the laboratory between 
every two experiments to remove all traces of impurities, probably in some 
cases it 
had not become perfectly cold before a new experiment was made, and hence the apparent irregularities in 
the results. As, however, this investigation forms the subject of a 
future paper, it is unnecessary to say more now 
than to remark that in all the results 
mentioned in this communication, the mercury was not used until its tempera- 
ture had become approximately that of the air. 
13/3/78 . 
Platinum. 
Mercury. 
16 
+ 0-129 
Copper. 
ii . 
16 
+ 0-316 
14/3/78 . 
». 
>> . 
15 
+ 0-254 
>J ... 
Very clean mercury . . . 
15 
+ 0-312 
15/3/78 . 
Zinc. 
Saturated zinc sulphate . . 
16 
-0-420 
Saturated zinc sulphate . . 
Saturated copper sulphate . 
16 
+ 0-095 
Zinc. 
1 of distilled water, 3 of 
16 
-0-444 
saturated zinc sulphate. 
