May 30, 1884.] 
ed, and in the table the figures in the top line 
are for the north and south polar zones. 
Those adjoining each are given next, so that 
the lower line contains the zones immediately 
north and south of the equator. Zones on 
the same line are at the same distance from 
the north and south poles respectively. 
The columns give the number of comets 
whose points of apparent origin fall in each 
zone, and the mean of the perihelion distances 
of the group. 
Sa La 
NORTH. SouTH. 
e | Mean perihelion Mean perihelion 
No. | arene! No. eieitnes: 
| 0.730 16 0.599 
8 1.022 13 0.713 
in 0.745 14 0.715 
12 0.700 13 0.526 
15 0.838 28 0.795 
14 1,010 11 1.008 
20 0.821 17 0.813 
11 } 0.903 10 1.091 
19 0.767 12 0.789 
15 0.762 15 0.912 
So many conditions that will readily occur 
to any one come in to affect the number of 
comets discovered, and, to a certain extent, 
the discovery of those coming from any par- 
ticular quarter, that the collection of so small 
a proportion cannot give much satisfaction. 
It will be noticed that the zones farthest south 
have a larger number than the corresponding 
zones north, while near the equator this differ- 
ence is reversed. 
The mean perihelion distances, taking the 
columns separately, vary in such a way that 
there is little encouragement for discussion as 
a whole. 
But taking the corresponding zones in the 
two hemispheres, the comparison is interesting, 
if not instructive. The first seven from the 
north pole, or direction of solar motion, down- 
ward, have greater mean perihelion distances 
than those in the southern hemisphere simi- 
larly situated. The equatorial zones, where 
the distinction would not be so great, have an 
opposite difference. 
With the same data combined in other pro- 
portions, the differences will be found to con- 
firm the tendency shown by this division. 
Thus doubling the area of the zones, making 
five northern and five southern, the excess of 
mean perihelion distances of the north over 
the south exists in the three polar sets. Com- 
parisons can also be made by fours and fives, 
and also by combining the two adjacent to the 
polar zones, the three next following these, and 
finally the four next north and south of the 
SCIENCE. 
651 
equator. Any one can make these compari- 
sons with small uncertainty, from the table. 
The most satisfactory confirmation of the 
tendencies here indicated is found in the dis- 
cussion of the comets of the last hundred years 
only. These have been well observed in gen- 
eral, and the number does not contain so large 
a proportion of anomalous orbits. The table 
above includes all, probably, that have been 
computed ; but, in summing up, notice was 
taken of the effect of the unusual cases, like 
the large perihelion distance of the 1729 comet, 
and the combination of several very small dis- 
tances in one zone; and in no case would the 
sign of the compared difference have been 
changed by the omission of any extraordinary 
comets. 
For the one hundred years the numbers in 
the zones are more uniform, with a similar ten- 
dency to that above. 
In the comparison of perihelion distances 
by zones, seven of the northern exceed the 
corresponding southern. 
The general results may be summed up in a 
few lines. ‘There is an indication that more 
comets come in from the hemisphere from 
which the sun is moving. 
The zones in the hemisphere towards which 
the sun is moving, and which has for its pole 
the direction of solar motion, have in general 
greater perihelion distances than the corre- 
sponding zones in the other hemisphere; the 
tendency being best exhibited as we go from 
the equator of the system. 
As the sun moves on, the comets at great dis- 
tances would come into the system, eventually, 
behind the quarter in which they first yielded 
to the attraction. Under the same general 
conditions, those which have come from behind 
the sun, and have been, as it were, dragged in 
its train, would pass nearest to the point of 
attraction when overtaking it. 
These are the suggestions which most natu- 
rally occur. A complete discussion of the ef- 
fect of the solar motion upon the distribution 
of comet-origins can hardly receive any de- 
cided confirmation with the amount of material 
that is likely to be available for generations to 
come. R. H. Tucker, Jun. 
Lehigh university. 
VOLCANIC SAND WHICH FELL AT UNA- 
LASHKA, ALASKA, OCT. 20, 1883, AND 
SOME CONSIDERATIONS CONCERN- 
ING ITS COMPOSITION. 
Mr. AppLecate, the signal-service obsery- 
er at Unalashka, reports that on the 20th of 
