5io 
Mr. Babbage on electrical 
Soon after the commencement of the experiment a mist 
arose within the case, which continued about five or six 
minutes : this frequently happened in the other experiments., 
The duration of the observations was about twenty-five 
minutes in the two preceding experiments. 
On examining the column of the mean point of the needle, 
I am not inclined to draw any inference respecting it : what- 
ever action may have been exerted on it, does not appear to 
have produced a marked or decisive effect on that point. I 
was induced to insert them, from the circumstance of the 
remarkable and gradual increase of the arc of vibration in 
both instances. This will be observed on looking down the 
columns of half differences, which is, in fact, the amplitude 
of each oscillation about the mean point. 
The observed retrograde movement in the eleventh expe- 
riment being so small, and yet exceeding many times the 
greatest possible error of observation, I was now desirous of 
enquiring whether, amongst the accidental circumstances to 
which the needle was exposed, there might not be found 
some one to whose influence this apparent anomaly might be 
ascribed. The number of causes to which it might be attri- 
buted was considerable ; but I hoped by variations in the 
circumstances of the experiment gradually to eliminate them. 
The following list comprised the greater part of them. 
The reverse motion might arise from, 1. Currents of air in 
the room; 2. From currents of air excited within the appa- 
ratus ; 3. By air driven through the gauze screen ; 4. By 
heated air rising from the metal plate heated by the lamp ; 
5. By the vibration excited in the apparatus by the motion of 
the jack ; 6. By the torsion of the silver wire to which the 
