47 
At any rate, it is certain that the appearance of streamers, 
the rapidity of change and emission, the perfect transparency 
and the wave-like fluctuations which belong to these phe- 
nomena, are all exhibited by the electric brush ; in fact, the 
electric brush will explain all these appearances which have 
defied all attempts at explanation on a material hypothesis. 
I have only to add that the main assumption involved in 
the electric theory is, that space is occupied by matter 
having similar electrical properties to those of gas; and 
I would ask, is it not more rational to make such an as- 
sumption than it is to attribute unknown and inconceivable 
properties to cometary matter ? 
Theories even, if founded only on rational speculation, 
often, I believe, prove very useful, insomuch as they afford 
observers a definite purpose in their observations — something 
to look for, something to establish or to refute; and I publish 
these speculations of mine at this particular moment in the 
hope that they may perchance serve such a purpose. 
“On Iso-di-naphthyl,” by "Watson Smith, F.C.S. Com- 
municated by Professor Roscoe, F.R.S. 
About the commencement of the month of March, 1870, 
when endeavouring, on the suggestion of Mr. John Barrow, 
in whose laboratory I was then engaged, to obtain anthra- 
cene by the action of a red heat upon naphthalin, the 
vapour of this body being passed through a red hot tube : 
I found that instead of the anticipated result occurring, 
according to the equation 7C 10 H 8 = 5C U H 10 + 6H, a body was 
obtained which had a melting point and also a boiling point 
pretty nearly agreeing with those of anthracene, but almost 
all its other properties were dissimilar to those characterising 
that body. 
This substance I found to fuse at from 200° to 204° C., 
its boiling point lying over that of mercury considerably, 
and also over that of anthracene as nearly as I could judge. 
