PROGRESS OP METEORIC ASTRONOMY IN AMERICA. 305 
If the existence of the comet as a member of the solar sys¬ 
tem antedates the meteor stream, it is difficult to see how the 
comet could have remained intact long enough to have been 
observed, in the presence of forces that for thousands of years 
have been transforming the figure of the original mass and 
stretching it out into a stream whose length is measured by 
hundreds of millions of miles. It is not improbable that 
comets of large dimensions are destroyed by the action of 
such forces; but that a body of that character should mi¬ 
raculously survive its own destruction and be found existing 
in ordinary cometary form in the midst of its own ruins is 
a proposition that makes large demands on the imagination. 
If the brightness of comets is caused by the vaporization 
of iron or stony matter, it must be produced by collisions 
between the masses at such. velocities that a high tempera¬ 
ture is developed, producing an incandescent vapor yielding 
a distinctive spectrum. It seems difficult to explain how 
such relative velocities can arise among the individual 
members of the same stream moving in a common orbit. 
It is more than probable that the light of a star passing from 
the extremely low temperature of space through the supposed 
high temperature of the comet’s nucleus, and again into the 
temperature of space, would suffer so much apparent change 
of position that it would compel recognition. It is claimed, 
however, that the individual masses of meteoric matter which 
form the nucleus are so far separated that the light of a star 
can pass through the aggregated mass without material 
change of direction. 
But if the masses are vaporized by collisions, then there 
must be absolute contact, which would to a great extent 
obstruct the passage of stellar light and would be certain 
to produce refraction. 
Lockyer’s Theories .—before leaving the consideration of 
these points I venture to call attention for a moment to a 
recent theory which has been set forth with considerable 
elaboration of detail. 
