354 
NATURE 
| (Feb. 9, 1882 
“organic radicals on the potas-ic compound of pyrol, by Signori 
Ciamician and Dennatedt.—Contributions to the anatomy of 
leaves (continued), by S. Briosii—On linear differential equa- 
tions, by S. Casorati. 
La Natura, January, 1882.—Considerations on some relations 
between the velocity of efflux, the specific heat, and the mean 
squares of the molecular velocity of gases, by Dr. Nachs.—On 
the rapidity with which light modifies the electric resistance of 
selenium, by Prof, Bellati and Dr. Romanese.—(9n the products 
of electrolysis of various acid and alkaline solutions, with 
graphite electrodes, by Dr. Bantoli and Regrasogli. 
LONDON 
Royal Society, December 8.— ‘‘ The Vibrations of a Vortex 
Ring, and the Action of Two Vortex Rings upon each other.” 
by J. J. Thomson. 
The first part of the paper contains a discussion of the vibra- 
tions which can occur in the figure of a vortex ring, whose 
cross-section is small compared with its aperture. It is proved 
that if the equations to the circular axis of a vortex ring are— 
p—a+an cos nt 
2=Bx cos nt 
p being the distance of a point on the circular axis from the 
straight axis, and 2 the distance of the point from the mean 
plane of the circular axis, then— 
> we" 2e — 
an = A cos (= log > Jn -1 +B) 
A Jn? -1 
2 — 
Bn a log = n Jn?-1 1+) 
where w is the angular velocity of molecular rotation, and ¢ the 
the radius of the cross-section of the vortex core; ¢ is small 
compared with a. 
Thus the time of vibration for such a displacement in the 
circular axis is— 
we” 
2a” 
ot if 7 be the velocity of the vortex— 
=2ma/ Tn, 72-1 
2é 
2n/ log sai Vn" -1 
This shows that a vortex ring with small cross-section of core 
is stable for all displacements of its circular axis. Sir W. 
Thomson bas proved that it is stable for all alterations in the 
shape of the cross-section of its core. 
The second part of the paper contains an investigation of the 
action of two vortices upon each other when the shortest distance 
between them is large compared with the diameter of either of 
the vortices. The amount of the disturbance each vortex 
experiences is worked out in the paper, but it may be sufficient 
to quote here the general effect of the collision which is given 
by the following rule :—the vortex which first passes through 
the point of intersection of the direction of motion of the two 
vortices is deflected towards the direction of motion of the 
other, it increases in radius and energy, aud its velocity of 
translation is diminished, the other vortex is deflected in the 
same directiou as the first, it diminishes in radius and energy, 
and its velocity of translation is increased. 
"On Melting Point.” By E. J. Mills, D.Sc, F.R.S. 
(Abstract.) 
The author gives a list of twenty-three aromatic compounds, 
the melting-points of which he has determined in terms of the 
air thermometer. The average probable error of a single result 
is about 0°7015. The numbers obtained, which range from 42° 
to 121°, obviously represent a set of thermometric standards, 
free from most of the grave inconveniences presented by the 
ordinary mercury-glass thermometer. In some cases they are 
shown to be proportional to the numerical value of the formula, 
a law which, it is suggested, may be in the limit the real law of 
melting-point. The original memoir contains a full description 
of apparatus and methods. 
Royal Society, January 12.—‘‘On the results of Recent 
Explorations of Erect Trees containing Reptilian Remains in the 
Coal Formation of Nova Scotia,” by J. W. Dawson, C.M.G., 
LL.D., F.R.S., &c. 
The explorations referred to were carried on chiefly in the 
beds at Coal Mine Point, South Joggins, Nova Scotia; and 
their object was to make an exhaustive examination of the con- 
tents of erect trees found at that place and containing remains of 
Batrachians and other land animals. e 
A detailed section is given of the beds containing the erec 
trees in question, with lists of their fos-il remains. The most 
important part of the section is the following :— 
Ft. In. 
Sandstone with erect Calamites and Stigmaria roots 6 6 
Argillaceous sandstone, C2lamites, Stigmaria, and 
Alethoptiris Cuchitica ie Get a a ee ee 
Gray scale, with numerous fossil plants, and “also 
Nataidites, Carbonia, and fish scales ... ... 1. 2 4 
Black coaly shale, with similar fossils ... ... .. I I 
Coal, with impressions of Sigé//aria bark o 6 
On the surface of the coal stand many erect Sigi//aria, pene- 
trating the beds above, and some of them nearly three feet in 
diameter at the base and nine feet in height. In the lower part 
of many of these erect trees there is a deposit of earthy matter, 
blackened with carbon and vegetable remains, and richly stored 
with bones of small reptiles, land snails, and millipedes. De- 
tailed descriptions of the contents of these trees are given, and 
it is shown that on decay of the woody axis and inner bark they 
must have constituted open cylindrical cavities, in which small 
animals sheltered themselves, or into which they fell and re- 
mained imprisoned. These natural traps must have remained 
open for some time on a sub-aerial surface. 
In all twenty-five of these erect trees had been discovered and 
extracted, and the productive portions of them preserved and 
carefully examined. Of these fifteen had proved more or less 
productive of animal remains. From one no less than twelve 
reptilian skeletons had been obtained. In a few instances not 
only the bones, but portions of cuticle, ornamented with horny 
sca'es and spines, had been preserved. 
The Batrachians obtained were referred to twelve species in 
all. Of these two were represented so imperfectly that they 
could not be definitely characterised. The remaining ten were 
referable to the two family groups of Microsauria and Lady- 
rinthodontia. 
The AMicrosauria are characterised by somewhat narrow 
crania, smooth cranial bones, simple or non-plaited teeth, well- 
developed limbs and ribs, elongated biconcave vertebra, bony 
seales ani plates on the abdomen, and horny scales, often 
ornate, on the back and sides. They show no traces of gills. 
The species belonging to this group are referred to the genera 
Hylonomus, Smilerpeton, Hylerpeton, and Fritschia. The cha- 
racters of these genera and of the several species are given in 
detail and illustrated by drawings and photographs, including 
microscopic delineations of the teeth of all the species, with their 
internal structure and the microscopic structure of their bones, 
as well as representations of their cuticular ornamentation and 
armour. 
The Labyrinthodonts are represented by only two species of 
Dendrerpeton, which are also described and delineated. 
About half of the reptilian species described are new, 
ani those previously described from fragmentary remains are 
now more fully characterised, and their parts more minutely 
examined, 
The invertebrate animals found are three species of land snails 
and five of myriapods, besides specimens supposed to represent 
new species of myriapods and insect larvae, not yet fully 
examined, and which have been placed in the hands of Dr. 
Scudder, of Cambridge, U.S. 
The memoir, consisting in great part of condensed descriptions 
of the facts observed, does not admit of much abridgment, and 
cannot be rendered fully intelligible without the accompanying 
plans, sections, and drawings. It closes with the following 
general statement :— 
‘*The negative result that, under the exceptionally favourable 
conditions presented by these erect trees, no remains of any 
animals of higher rank than the A/icrosauria and Labyrintho- 
dontia have been found deserves notice here. It seems to indi- 
cate that no small animals of higher grade inhabited the forests 
of Nova Scotia at the period in question; but this would not 
exclude the possibility of the existence of bigher animals of a 
larger size than the hollow trees were capable of receiving. Nor 
does it exclude the possibility of higher animals haying lived 
contemporaneously in upland situations remote from the low 
flats to which our knowledge of the coal formation is for the 
mo t part confined, It is to be observed also that as some of 
