650 SCIENCE. 
light, make the stone a remarkable freak of 
nature; and not a little interest is added to it 
by the fact that its strange features were so 
well developed by mere accident. 
Among curiously marked diamonds resem- 
bling the above, may also be mentioned the 
two presented to the Jardin des plantes by 
Halphen, and described by Descloizeaux (see 
Poggendorff’s annalen, 1849, ix. p. 447). 
These stones are colorless and round, and a 
distinct three-leaved clover in black occupies 
the entire dimension in each stone. Another 
in the Duke of Leuchtenberg’s cabinet, now in 
the Bavarian state cabinet at Munich, has 
three leaves united by a circle. All these three 
are of Indian origin. 
A curious diamond (fig. 6), also in the pos- 
session of Messrs. Tiffany and Co., is a red 
brilliant, that at first glance appears brown, 
while through it a beautiful dark rose-red light 
breaks in every direction: really, therefore, it 
is a red brilliant, or combination of red and 
brown; or, more correctly, a red diamond with 
a brown cloud, the red predominating as the 
stone is turned, or the light strikes it in differ- 
ent directions. ‘This change of color gives the 
stone its dichroitic effect, although no effect is 
produced in viewing it by the dichroscope. 
By artificial light it appears brown; but the 
entire stone throws out bright red reflections, 
such as are produced by the diamond only. 
One-half of the stone is filled with hundreds 
of irregular-shaped cavities, either empty, or 
filled with a transparent fluid, or, as in nearly 
all cases, with carbon, which in some instances 
1s in pieces, or so fractured as to admit the 
light through it. These inclusions appear to 
affect the color sufficiently to produce the 
brown appearance. 
Light seems to be very faintly restored under 
the crossed Nichols prisms, in addition to that 
produced by the cutting of thegem. The spe- 
cific gravity is 3.5696. GrorcEe F. Kunz. 
THE DISTRIBUTION OF COMETS WITH 
REFERENCE TO SOLAR MOTION. 
THE regions of space outside the solar sys- 
tem furnish a supply of comets which seems to 
be inexhaustible. Their origin is simply a mat- 
ter for speculation ; and it is not reasonably to 
be expected, that, even with the large amount 
of attention being given to cometary investiga- 
tion, any definite information upon this subject 
can be attained for centuries to come. There 
is no probability that any considerable number 
of them have had their origin in the mass 
which has gone to form the solar system. 
Between six and seven hundred comets have 
been recorded ; and if we take the large pro- 
portion of telescopic comets which have been 
discovered when searching has been vigor- 
ously prosecuted, to the number visible with- 
out the aid of a telescope, it would not be an 
exaggerated estimate to place the number of 
comets which have come into our system since 
the beginning of the Christian era, under such 
conditions as to have been visible by the aid 
of our modern appliances, at four thousand. 
Undoubtedly there are many, which, either 
from their small size and faintness, or from 
the unfavorable positions of their orbits, never 
could be seen. Were the orbits of all these 
known, the discussion would furnish some rea- 
sonable basis for an hypothesis in regard to 
the origin of the comets themselves ; and light 
would be thrown upon other problems concern- 
ing the system of the universe. 
While the sun, drawing all bodies within its 
influence towards itself, swings the comets into 
orbits which may bring them, at some point, 
almost into contact with the sun’s surface, or, 
on the other hand, never within the confines 
of our planetary system at all, the motion of 
the sun itself must have an influence upon the 
position of these orbits. The limited amount 
of material at hand furnishes some features 
which are at least suggestive. 
There are two hundred and eighty-five com- 
ets, which, up to the present time, have had 
their orbits determined with greater or less 
exactness. ‘The axes of the orbits lie in the 
directions along which the comets come to 
the sun. 
The table exhibits the grouping of the points 
which represent the directions of the origins of 
these comets about that point which investi- 
gation has indicated as the direction to which 
the solar system is moving. 
The method of making the reductions will 
be apparent. The elements were reduced to 
1850, and the longitude and latitude of the 
perihelion point computed for each comet. 
The point directly opposite this was then re- 
duced to a new system of co-ordinates, having 
the direction of solar motion, as the pole. 
The point toward which the sun is moving 
is taken at longitude 256°, latitude +57°. 
For convenience this may be referred to as 
the north pole of the new system; and the 
hemisphere surrounding it, as the northern. 
This hemisphere is then divided into ten zones 
of equal area, the most northern surrounding 
the pole, while that at the base may be called 
the equatorial. 
The southern hemisphere is similarly divid- a 
[Vou. IIL, No. 69. 
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