530 
NATURE 
[ Sept. 30, 1886 
tures, infiltrations, and apparent faultings seen in microscopic 
sections and by the naked eye—these all imply the action of 
force. M. Daubrée supposes that the union of oxygen and 
silicon furnishes sufficient heat for making these minerals. If 
this is possible, those transformations may have taken place in 
their first home. Dr. - Reusch argues that the repeated heating 
and cooling of the comet, as it comes down to the sun and goes 
back again into the cold, is enough to account for all the peculi- 
arities of structure of the meteorites. These two modes of action 
do not, however, exclude each other. Suppose, then, a mass 
containing silicon, magnesium, iron, nickel, a limited supply of 
oxygen, and small quantities of other elements, all in their prim- 
ordial or nebulous state (whatever that may be), segregated 
somewhere in the cold of space. As the materials consolidate 
or crystallise, the oxygen is appropriated by the silicon and 
magnesium, and the iron and nickel are deposited in metallic 
form. Possibly the heat developed may, before it is radiated 
into space, modify and transform the substance. The final result 
is a rocky mass (or possibly several adjacent masses), which 
sooner or later is no doubt cooled down.throughout to the tem- 
perature of space. This mass, in its travels, comes near to the 
sun. Powerful action is there exerted upon it. It is heated. 
How intense is that heat upon a cold rock, unprotected appar- 
ently by its thin atmosphere, it is not possible to say. We know 
that the sun’s action is strong enough to develop that immense 
train, the comet’s tail, that sometimes spans our heavens. It is 
broken in pieces. We have seen the portions go off from the 
sun, to come back, probably, as separate comets. Solid frag- 
ments are scattered from it to travel in their own independent 
orbits. What is the condition of the burnt and crackled surface 
of a cometic mass or fragment as it goes out from the sun again 
into the cold? What changes may not that surface undergo be- 
fore it comes back again, to pass anew through the fiery ordeal ? 
We have here forces that we know are acting. They are in- 
tense, and act under varied conditions. The stones subject to 
those forces can have a history full of all the scenes and actions 
required for the growth of such strange bodies as have come 
down tous. Some of our meteors, those of the star-showers, 
have certainly had that history. What good reason is there for 
syne that all of them may not have had the like birth-place and 
ife ? 
The pieces which come into our air in any recurring star- 
shower belong to a group whose shape is only partly known. It 
is thin, for we traverse it ina short time. It is not a uniform 
ring, for it is not annual, except possibly the August sprinkle. 
How the sun’s unequal attraction for the parts of a group acts as 
a dispersive force to draw it out into a stream, those most beauti- 
ful and most fruitful discussions of Signor Schiaparelli have 
shown. ‘The groups that we meet are certainly in the shape of 
thin streams. 
It has been assumed that the cometic fragments go continu- 
ously away from the parent mass, so as to form, in due time, a 
ring-like stream of varying density, but stretched along the entire 
elliptic orbit of the comet. The epochs of the Leonid star- 
showers in November, which have been coming at intervals of 
thirty-three years since the year 902, have led us to believe that 
this departure of the fragments from Tempel’s comet (1866, I.) 
and the formation of the ring was a very slow process. The 
meteors which we met near 1866 were therefore thought to have 
left the comet many thousands of years ago. The extension of 
the group was presumed to go on in the future until, perhaps 
tens of thousands of years hence, the earth was to meet the 
stream every year. Whatever may be the case with Tempel’s 
comet and its meteors, this slow development is not found to be 
true for the fragments of Biela’s comet. It is quite certain that 
the meteors of the splendid displays of 1872 and 1885 left the 
immediate vicinity of that comet later than 1840, although at the 
time of those showers they had become separated two hundred 
millions of miles from the computed place of the comet. The 
process, then, has been an exceedingly rapid one, requiring, if 
continued at the same rate, only a small part of a millennium for 
the completion of an entire ring, if a ring is to be a future form 
of the group. 
It may be thought reasonable in view of this fact about Biela’s 
comet, established by the star-showers of 1872 and 1885, to re- 
vise our conception of the process of di integration of Tempel’s 
comet also. The more brilliant of the star showers from this 
comet have always occurred very near the end of the thirty- 
three year period. Instead of there being a slow process 
which is ultimately to produce a ring along the orbit of 
the comet, it certainly seems more reasonable to suppose 
that the compact lines of meteors which we met in 1866, 
1867, and 1868 left the comet at a recent date. A thousand 
years ago this shower occurred in the middle of October. By 
the precession of the equinoxes and the action of the planets, 
the shower has moved to the middle of November. One half 
of this motion is due to the precession, the other half to the 
perturbing action of the planets. | Did the planets act upon the 
comet before the meteoroids left it, or upon the meteoroid 
stream? Until one has reduced the forces to numerical values, 
he may not give to this question a positive answer. , But I 
strongly suspect that computations of the forces will show that 
the perturbations of Jupiter and Saturn upon that group of 
meteoroids hundreds of millions of miles in length,—perturba- 
tions strong enough to change the node of the orbit 15° along 
the ecliptic, —would not leave the group such a compact train 
as we found it in 1866. 
because the total action is scattered over so many centuries. But 
it seems more probable that the fragments are parting more 
rapidly from the comet than we have assumed, and that, long 
before the complete ring is formed, the groups become so scat- 
tered that we do not recognise them, or else are turned away so 
as not to cross the earth’s orbit. 
Comets, by theirstrange behaviour and wondrous trains, have 
given to timid and superstitious men more apprehensions than 
have any other heavenly bodies. They have been the occasion 
of an immense amount of vague, and wild, and valueless specu- 
lation by men who knew a very little science. They have 
furnished a hundred as yet unanswered problems which have 
puzzled the wisest. A world without water, with a strange and 
variable envelope which takes the place of an atmosphere, a 
world that travels repeatedly out into the cold and back to the 
sun, and slowly goes to pieces in the repeated process, has con- 
ditions so strange to our experience, and so impossible to repro- 
duce by experiment, that our physics cannot as yet explain it. 
But we may confidently look forward to the answer of many of 
these problems in the future. Of those strange bodies, the 
comets, we shall have far greater means of study than of any 
other bodies in the heavens. The comets alone give us speci- 
mens to handle and analyse. Comets may be studied, like the 
planets, by the use of the telescope, the polariscope, and the 
spectroscope. The utmost refinements of physical astronomy 
may be applied to both. But the cometary worlds will be also 
compelled, through these meteorite fragments,—with their in- 
cluded gases and peculiar minerals,—to give up some additional 
secrets of their own life, and of the physics of space, to the 
blowpipe, the microscope, the test-tube, and the crucible. 
THE BRITISH ASSOCIATION ~ 
SECTION D—BroLocy 
Initiation of a Discussion upon the Value of the ‘* Type- 
system” in the Teaching of Botany, by Prof. Bayley Balfour.— 
‘The speaker remarked that within the last fifteen years there had 
been a complete revolution in the method of teaching botany 
and zoology. The old method was practical teaching based on 
classification. In fact, in the olden times it was taught by 
means of object-lessons, which were sporadically chosen. In 
that method the real significance of plant life was completely 
overlooked, and also the position of the plants in Nature and 
their relationship to the animal kingdom. ‘The result was that 
they had naturalists bred who had a wide range of knowledge 
of plant forms, and able to recognise and name a great number — 
of plants, but of the life-history and sequence of events they 
were in the dark. The knowledge was a wide but superficial 
one. The new system was the natural outcome of the progress 
of the science, and as more knowledge of the minuter forms 
were obtained, it became necessary to select individual forms to 
be made types for special study. Thus by degrees a system of 
teaching was introduced which consisted in the selection of a 
few characteristic forms, and those were thoroughly studied in 
their structural and physiological relationship. Thus accurate 
knowledge of a few types was obtained, and the work now, in- 
stead of being in the field, was transferred to the laboratory. 
‘Yhat new method was greatly used at the present time, and 
promised to be more widely introduced by the publication of 
new text-books running along the lines of that teaching. The 
old system he did not think produced good results, but he ~ 
thought that teaching from types, combined with a certain 
amount of old teaching, would be effective. 
If this result is at all possible, it is- 
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