44 
ordinary emanation. As they continue to recede from the 
sun their motion diminishes and their tail dies away, or is 
absorbed into the head, which itself grows continually 
feebler, and is at length altogether lost sight of.” 
Here, although unconsciously, Herschel has connected the 
increase of brightness with the increase of speed with which 
comets approach the sun, and the diminution in brightness 
with the diminution of the velocity with which they leave 
the sun. And although from Herschel’s remark just 
quoted it might be inferred that proximity to the sun is the 
cause of the increase of brightness, this is proved not to be 
the case, for (as in the case of Halley’s comet) when near 
its perihelion the tail always dies away, and the comet 
shrinks. Thus when the comet is nearest to the sun there 
is no development of tail, which shows clearly that it is not 
the intensity of the sun’s rays but the change in their inten- 
sity that is the exciting cause of these extraordinary appear- 
ances. So that there is no reason to suppose that a planet 
composed of the same material as a comet, no matter how 
close to the sun, would show a vestige of tail or other 
cometic appearance. 
It is then to this change in position that we must attri- 
bute those peculiar appearances which belong to comets. 
Now, is not electricity the very effect which would natu- 
rally result from such a state of change and variation in 
condition ? 
A. De la Rive remarks, “ Electricity is one of the most 
frequent forms which the forces of nature assume in their 
transformations. It certainly often accompanies a change 
in temperature. There is every indication that it is so in 
our atmosphere, for the times when its intensity is a 
maximum are just after sunrise and just after sunset, both 
winter and summer. 
From these reasons it seems to me not only possible’ but 
probable that these strange visitors to our system are clothed 
