ON ELECTRICAL OBSERVATIONS AT KEW. 117 
> TABLE III. 
‘Number of negative readings at each observation-hour in the three years 
: 1845, 1846 and 1847. 
Year.|Mid.|2 a.m.|4 a.m.!6 a.m.|8 a.m./10 a.m.|Noon.|2 p.m.|4 p-m.|6 p.m./8 p-m.|10 p.m./Sums, 
—_— 





5) 5 11 17 13} 16-} 22 | 20 | 17 15 | 149 
1846.) 1 4 4 5 9 18 11 ll 12 } 10 5 4 94 
I 1 4 9 11 10 | 13 7 9 5 8 81 


_—_—-_ 

a | | | es | een | | |) — |} —_. —| 
Sums.) 7 | 10 | 10 | 14 | 29 46 34 | 40 | 41 | 39 | 27 27 «(| 324 
See a a a ea ee a | 

The mode of discussion adopted has been, to arrange all the positive 
readings under the respective hours of observation, and then to divide their 
sums by the number of readings at each hour, so that the values recorded in 
the following tables are the arithmetical means of the readings at each ob- 
servation-hour. The transcription from the Journal has been most carefully 
checked, and every precaution taken to ensure accuracy, both in ascertain- 
ing the number of observations and in calculating the means; in the latter 
case the arithmetical operations have been executed in duplicate. The re- 
sults of these computations, as before mentioned, are expressed in terms of 
_ Volta’s standard electrometer No. 1, all observations of tensions exceeding 
the range of this instrument having been reduced to its readings (see de- 
scription of electrometers, ‘ Report,’ 1844, p. 124, and the previous note on 
p- 114 of this Report). 
On the Ist of January 1845, when the night-registering apparatus was 
first brought into use, a note occurs in the register which it is important to 
transcribe here. It is as follows :— 
“ The electric tensions at the hours 0, 2 and 4 are estimated by adding a 
quarter of a degree (of Volta) to the tensions exhibited by the three night- 
registering electrometers at sunrise, for each hour which has elapsed between 
the time at which they were charged (by the clock) and the time of observing 
them (viz. sunrise). 
*« The rate of loss by these electrometers begins to be inconstant after the 
tension has exceeded about 50° (of Volta): vde Experiments, 1844, p. — ; 
if, therefore, the tension at sunrise of any such instrument shall exceed 50°, 
it is not noted in the Journal*.” 
TABLE IV. 
Mean electrical tension at each observation-hour in the three years 1845, 
1846 and 1847, with the mean diurnal period as deduced from the whole. 



Year.|Mid. |2 a.m./4 a.m./6 a.m./8 a,m.|10 a.m.|Noon.|2 p.m./4 p.m./6 p.m.|8 p.m./10 p.m.|Mean. 











‘ div.| div. | div. | div. | div. |* div. div. | div. div. div. div. div. diy. 
1845.)19°8 | 17-8 | 18-3 | 28°6 | 64:7 | 84:4 |67°9 | 59-9 | 59-2 | 71-1 | 98°9| 117-2 | 63:1 
1846./24°3 | 21°2 | 21°4 | 35-4 | 61-1 76°7 |69°6 | 65°5 | 63-5 | 85°0 | 96°3| 87:2 | 61:3 
1847.)23°7 | 21-1 | 21-5 | 38-7 | 78°7 | 102-5 | 88:4 | 89-4 | 85-0 | 99-1 |112:°0|107°9 | 76:3 






Mean.|22°6 | 20-1 | 20-5 | 34:2 | 68-2 | 88-1 | 75'4 | 71'5 | 69-1 | 84:8 |102-4 | 104-0 | 66-9 
‘ * For a full description of these night-registering electrometers, see ‘ Report,’ 1844, p. 138, 
under the head of “ Experiments on insulation by means of chloride of calcium.” 
