60 Observations on some Experiments in Electricity. 
ness and height of the wick and about a quarter of an inch in breadth. 
In some instances the candle was actually extinguisned by the current. 
4. Length of sparks as affected by the size of balls. 
In making some experiments upon the length of sparks as depen- 
dent on the-size of balls between which they passed, the following 
among other results were obtaine 
Two conductors, in all onpebi alike and equally well insulated, 
furnished at one end of éach, with a ball two and a half inches in 
diameter, and at the other end with one of six and a half inches, 
were placed, one in connexion with the rubber and the other with 
the collecting points, having the end of each which was farthest from 
the machine, brought into such proximity as to transmit the spark. 
When both the small balls were brought together, the spark they 
gave was 9.8 inches long, exhibiting a bright light for about an inch, 
near the negativé ball, and a pale purple line through the rest of the 
course. On reversing the ends of the negative conductor, the other 
remaining as before, the length of the spark was not sensibly altered, 
but on bringing the six inch ball of the positive conductor near the 
negative one of the same size, the greatest striking distance was five 
and a half inches, and the same when the negative conductor was 
again reversed so as to send the spark between the two and a half 
negative and the six inch posttive balls. 
. The season most favorable to electrical experiments. 
It is a common opinion that electrical experiments cannot be suc- 
cessfully executed except in cold weather. Buta little reflection 
will assure one that the action of electricity, so far as the state of the 
air is concerned, is dependent chiefly on the relation between the 
thermometric and the hygrometric states of the atmosphere; in other 
words, on the elevation of the temperature above the dew-point. 
Hence the direction to warm the machine and apparatus before we 
attempt experiments; to wipe the insulators with warm cloths, &c. 
It would be of little use to wipe moisture from a glass, if the article 
wiped were left of a temperature to condense moisture from the sur- 
rounding air. Hence too the utility of artificially heating the apart- 
ment in which we operate, as we thereby produce a local atmosphere, 
with a considerable range between its dew-point and its actual tem- 
perature. In this manner I have often succeeded in experiments on 
jars and batteries in a close room, while it was actualy raining with- 
out. But it must be understood that the success will depend on the 
