SCIENCE. 
293 
ous wings and were probably aquatic in early life. The 
last statement is simply inferred from the fact that all the 
modern types most nearly allied to them are now aquatic. 
“ Some of the Devonian Insects are plainly precursors of 
existing forms, while others seem to have left no trace. 
The best examples of the former are Platephemera, an 
aberrant form of an existing family ; and Homothetus which, 
while totally different in the combination of its characters 
from anything known aiming living or fossil insects, is the 
only Palaeozoic insect possessing that peculiar arrangement 
of veins found at the base of the wings in Odonata typified 
by the arculus, a structure previously known only as early 
as the Jurassic. Examples of the latter are Gerephemera, 
which has a multiplicity of simple parallel veins next the 
costal margin of the wing, such as no ether insect ancient 
or modern is known to possess ; and Xenoneura, were the 
relationship of the internomedian branches to each other 
and to the rest of the wing is altogether abnormal. 
“ If, too, the concentric ridges, formerly interpreted by 
me as possibly representing a stridulating organ, should 
eventually be proved an actual part of the wing, we should 
have here a structure which has never since been repeated j 
even in any modified form. 
<• They show a remarkable variety of structure, indicating 
an abundance of insect life at that epoch. 
“The Devonian Insects also differ remarkably from all 
other known types, ancient or modern ; and some of them 
appear to be even more complicated than their nearest liv- 
ing allies. 
" We appear, therefore, to be no nearer the beginning of 
things in the Devonian epoch than in the Carboniferous, so 
far as either greater unity or simplicity of structure is con- 
cerned ; and these earlier forms cannot be used to any bet- 
ter advantage than the Carboniferous types in support of 
any special theory of the origin of insects. 
“ Finally, while there are some forms which, to some de- 
gree, bear out expectations based on the general derivative 
hypothesis of structural development, there are quite as 
many which are altogether unexpected, and cannot be ex- 
plained by that theory without involving suppositions for 
which no facts can at present be adduced.” 
MICROSCOPY. 
Mr. W. H. Bullock, of Chicago, the maker of the micro- 
scope for lithological work described by us in Vol.. I, No. 
21 of Science, writes to us, objecting to an editorial remark, 
that the arrangement of the polariscope for instant use, 
claimed as a novelty by Mr. Bullock, had been used in 
the same position by Swift, of London, for many years. 
Mr. Bullock admits the accuracy of this statement, but 
now sends details, as evidence, that he has shown consider- 
able ingenuity in arranging his analyzing prism, “mounting 
it in such a manner, that it can be turned round go degrees, 
so that when the lower prism is at the spring stop or zero 
point, and the upper prism is pushed into position with the 
indicator forward, the prisms are parallel, and upon its be- 
ing turned back or revolved go degrees the prisms are 
crossed.” “The lower prism is also arranged differently to 
that used by Swift ; it can be fitted either to the sub-stage 
or used in the supplementary sub-stage, and thus used close 
under the stage, so that no light can reach the object under 
observation, except that which passes through the lower 
prism.” Mr. Bullock also notices other improvements 
which must render the instrument very perfect for the pur- 
poses for which it was designed, namely, lithological work. 
Mr. Bullock sends a photograph of this microscope and 
we readily admit that it appears to be an excellent instru- 
ment ; of the workmanship we are, of course, unable to 
speak, but probably the reputation of Mr, Bullock is 
sufficient guarantee in this respect. 
New York Academy of Sciences. — Section of 
Chemistry. — Monday Evening, December 13, 1880, at 8 
o’clock, the following paper, by Dr. Henry A. Mott, is 
announced Chemical Decomposition incited by a Cold 
Fluid Stratum floating on a Warm Liquid. 
ASTRONOMY. 
JUPITER. 
MOTION OF SPOTS ON HIS SURFACE. 
Jupiter, always enigmatical, has, since the appearance 
of the great red spot in his Southern hemisphere, become 
more and more perplexing. It was supposed this object 
would afford a ready means of determining Jupiter’s true 
period of rotation. It has not done this, but has certainly 
led to the development of many interesting facts, one of 
which is that no period can be determined, because there 
are not two parts of the planet’s visible surface which 
rotate in equal times. It would seem leasonable that any 
two points on the same parallel of latitude and in the 
same hemisphere must necessarily rotate with equal 
velocities; this does not even hold good. Could we be 
placed in such a position that the rotation of the planet 
would not visibly change the position of objects on his 
surface, we should still see the spots moving not only 
with different velocities, but in contrary directions. Spots 
very rarely change their latitude, as the very great axial 
rotation of Jupiter confines their motion to a parallel 
with his equator. In Jupiter’s Southern hemisphere are 
two or three small dusky oblong spots. The most dis- 
tinct of these I first observed on the morning of July 25, 
1880, (see English Mechanic, No, 804, where an engrav- 
ing showing its position is given). This group of small 
spots lies on a parallel of latitude about even with the 
Southern edge of the great red spot. On July 25, the 
centre of the first observed of the spots preceded the 
centre of the large spot by ih. 35m. Since that date the 
red spot has been observed constantly, and the small one 
frequently. Up to November 23, thirty-five transits of 
the great spot across the central meridian, and nine of 
the smaller have been carefully observed. On November 
22, the small spot preceded the greater by 3h. 17m. 
The interval between their transits having increased ih. 
42m. since July 25. The large spot has moved backward, 
compared with the direction of rotation, making its 
transit on November 22 occur 49m. later than on July 25, 
while the small spot came to its transit 53m. earlier 
than on July 25, showing that the two are moving with 
nearly the same velocity, but in opposite directions. The 
mean daily drift backward of the great spot since July 
25 has been 0.40245m, while the forward motion of the 
small spot has been, during the same period, 0.43948m 
per day. It will be seen from this that a rotation derived 
from the small spot would indicate a quicker period than 
that derived from the large red spot. 
From the observations of July 25 and Nov. 22, the 
great spot rotates in 9h. 55m. 37.065s., and the small 
one in 9h. 55 m. 16. 176s. The mean rotation of the two 
is 9h. 55m. 26.621s. A reduction of all the observa- 
tions on hand will, doubtless, slightly change these figures. 
It would be well for observers to watch this small spot, 
as it may last as long as the large one. If it should con- 
tinue permanent, it will eventually make the circuit of 
Jupiter and meet the red spot ; this would occur about 
the middle of February, 1882. 
But the motion of these two objects is very slow com- 
pared with the rapidly moving black spots which appeared 
just north of the equatorial belt on the last of October. 
But as attention has already been called to these remark- 
able objects by Messrs. Dennett, Williams and Denning, 
in English Mechanic, No. 816, 1 will not refer to them 
here, further than to say that they have been observed 
and sketched as often as the weather would permit since 
their first appearance. The region occupied by the great 
equatorial belt is subject to constant and quite rapid 
J change, being filled at times with the most delicately soft 
plumey forms. Brilliant white spots are not unfrequent 
in this zone. These bright spots generally appear as m- 
| tensely white heads, followed by a light, diffused and 
j fainter train. Sometimes this train is composed of light, 
