ON ELECTRICAL OBSERVATIONS AT KEW. 16IE 
PR a et ae ee 
Ti is not so gracefully flowing in its character, although based on a greater 
_number of observations, thereby indicating a certain irregularity of move- 
ment in the monthly increase and decrease of tension, doubtless dependent 
_on the accidental electrical character of each individual month contributing 
~ to the mean, which accidental character, it is highly probable, is derived from 
certain disturbing influences to be noticed in the next section, the effects of 
which have been eliminated in the sunset curve by employing five instead 
of three years’ observations. The apex of the mean annual curve of 1845 to 
1847 occurs a month later, but from the high tension in January it would 
probably appear that from a longer series of observations, January and 
February would present an equality of tension, or January would become 
the superior. As it is, there is at this pointa marked difference between the 
curves, the later occurrence of the apex in the three years’ curve destroying 
to a great extent the symmetry so observable in the sunset curve. With 
the exceptions just noticed, the two curves in their general course are similar, 
and this would suggest that the sunset curve presents to a certain extent an 
approximation to the mean annual curve of electrical tension, but in excess. 
The monthly differences between the two are as follows. 
TABLE LXIX. 
Monthly differences between the annual periods at sunset (five years) and 
the mean of the years 1845, 1846 and 1847. 
Jan.| Feb.|Mar.| April.|May.| June.| July. |Aug.| Sept. | Oct.|Nov.|Dec.|Mean. 
mf ff i | | | ee a 
diy. | div. | div. | div. | div.| div. | div. | div. | div. | div. | div. | div. | div. 
+/—-|+i tft] +} +/+} 4+) +]4) 4) 4+ 
20-5) 41-8] 10°6] 11:0] 134) 12°9| 5:2 | 9°9 11°6 4°3 | 17-5] 17:9] 11°5 
: It will be observed that these differences upon the whole are greater in 
: winter than in summer, particularly in the months of November, December 
and January. During these months the epoch of sunset is nearer to 4 P.M. 
| than at any other period of the year, and at this hour the electrical tension 
differs only 2:2 div. from the mean, being in excess. If we take the curve 
of the three years as representing the mean tension, then it would appear 
that the mean tension at sunset increases upon the mean of all the observa- 
| tions at the twelve daily readings during the winter as compared with the 
summer, to the extent of about 16 div. The following numbers express the 
ratio of the mean tension derived from the observations atthe twelve obser- 
*  vvation-hours to the mean tension at sunset. 
Taste LXX. 
tio of the mean electrical tension, as derived from the observations of 1845, 
846 and 1847, to the mean electrical tension, as derived from five years’ 
observations at sunset for each month in the year. 
Jan.| Feb. |Mar.| April.|May.| June.| July. |Aug.| Sept.| Oct. |Nov.|Dec.|Mean. ‘ 
| af | | | | | a | me | | mn | ne 
*880| 1-334] *876| -838 |-738| °694| -881 |°748] +739 | -921) °799) -859) -853 

It will be observed that these ratios approach nearer to unity in the winter 
_ than in the summer, agreeing in this respect with the differences already 
“noticed ; but while the increasing differences denote divergence in the curves, 
_ the increasing ratios indicate a proportional convergence in the values of 
their ordinates. In winter the proportional value of the entire mean tension, 
1849. M 
ba! 

