i % B77 : , 
620 NATURE [APRIL.29, 1897 
. . . As development proceeds, and the skull begins to assume a | gravitating bodies in, space, and, taking everything into con- 
more fixed and rigid shape, new conditions and relations of the | sideration, it is quite surprising what good resul!s were 
growth forces take place, as a result of which those portions of 
the cerebral surface lying in the depths of some of the fissures, 
originally produced by depression, are placed under new dy- 
namical conditions ; instead of being situated as formerly along 
the lines of resolution of greatest pressure and least resistance, 
they become centres of relatively greatest growth force as com- 
pared with the resolution of pressure forces.”’ Ilence they rise 
up as annectant gyri. To these interesting, and at one time 
puzzling, features he devotes some pages. 
He gives a very brief, and second-hand, account of the con- 
volutions in Carnivora and Ungulata, rightly insisting that it is 
impossible to homologise these fissures, one by one, with those 
of Primates’ brains; for, even between ungulate and carnivore, 
it is only possible to compare groups of This fact is 
gradually becoming more and more fully recognised ; and in 
mounting a series of brains for the Oxford Museum, I have pur- 
posely indicated the fissures in the ungulate, for example, and 
the Primate brain, by means of entirely different sets of colours. 
There is a type of convolution for each order, these types being 
derived, not one from another, but independently for a smooth- 
brained condition ; a view which accords with paleontological 
evidence. Nevertheless, there is more community between the 
Ungulata and the Carnivora, in this matter, than between other 
groups, 
Finally, the author discusses the ‘* Mechanics of the for- 
mation of cerebral fissures,’ and brings to bear on the subject 
(a) the theory of the formation of films in soap-bubbles, pro- 
pounded by Plateau ; and (4) the facts of surface tension as put 
forward by Maxwell. This part of the paper is illustrated by 
numerous formulze and diagrams ; but I imagine most anatomists 
will pass these by. If for surface tension of films we substitute 
the pressure forces produced by cerebral swellings aggregating 
round certain centres, then the peripheries, meeting each other 
within a confined space, produce the lines of fissuration. 
The memoir, interesting as it is, would have been rendered 
more valuable by the addition of a bibliography ; references are, 
indeed, given here and there in footnotes, but they are scarcely 
worthy of the work. 
The figures, again, copied as many of them are from various 
sources, are variously lettered; there is practically no ‘‘ex- 
planation ” of plates, and some of the figures, which are mere 
outline drawings without shading, represent the brain in oblique 
directions, which it is very difficult to follow, as no indication 
of these directions is given in the list of figure 
W. B. 
issures. 
BENHAM. 
LECTURE-ROOM DEMONSTRATION OF 
ORBITS OF BODIES UNDER THE ACTION 
OF A CENTRAL ATTRACTION.' 
N 
JT remembering to have seen any attempt to show ex- 
perimentally in the lecture-room the motion of bodies 
acted on by a central attractive force varying inversely as the 
square of the distance in elliptic, parabolic and hyperbolic orbits, 
I have made a few experiments with a view of determining 
how well these curves could be imitated by the motion of a 
small steel ball around a magnetic pole. The results were so 
good that I feel warranted in making them known, and believe 
that the experiment may be found useful in making more 
cheerful that portion of the course usually rather destitute of 
pyrotechnics. 
The apparatus used was very simple, consisting of a circular 
glass plate about 40 cm. in diameter, with a small hole in the 
centre, through which projected the somewhat conical pole- 
piece of a large electro-magnet (Fig. 1). The surface of the 
plate was smoked, and it was made level as nearly as possible, 
the axis of the magnet being of course vertical. 
A small, highly-polished ball of steel about 5 mm. in diameter 
{from a bicycle bearing), when projected across the plate, traced 
its path in the soot, and left a permanent record of its motion, 
Under these conditions gravity exerts no direct influence on 
the motion, and we have only the initial velocity and the central 
attractive force to deal with, together with the loss of velocity 
due to friction. There are several other circumstances which 
make the conditions unlike those existing in the case of two 
Reprinted from the Physical Review, with supplementary note by the 
author 
NO. 1435, VOL. 55 | 
obtained. 
The ball was blown out of a short piece of glass tubing held 
in the plane of the plate with varying initial velocities, and 
curved orbits obtained, which were, at least, good imitations of 
the ellipse parabola and hyperbola. 
Fig. 2 is a photograph of a plate showing all three forms, 
the white spot in the centre being the hole occupied by the 
magnet pole ; the arrows indicate the direction of the motion. 
No. 1 was produced with low initial velocity, and is a 
very fair represention of an ellipse, with the attractive force in 
one focus. The loss of velocity due to friction caused the ball 
to ‘‘fall into the sun” after completing one revolution, a one 
year’s existence of the system. 
On another trial an ellipse (sfzvad, strictly speaking) was ob- 
tained that was almost re-entering, the miss being not more 
than a couple of millimetres, while in the one figured it was 
nearly a centimetre. 
The right-hand branch of No. 2 resembles a_ parabola, 
and was produced by a somewhat higher initial velocity. It 
will be noticed that the ball moved to its perihelion position 
in a path rather like a hyperbola, and on rounding the pole, its 
velocity having been diminished somewhat, moved off in a 
Fic. 2. 
parabola. It would be more exact, probably, i: we called this 
curve an ellipse of great eccentricity, since the conditions 
governing the formation of a parabolic orbit would be difficult 
even to approximate. ; 
No. 3 and 4 are hyperbole, produced by still higher initial 
velocities. 
None of the orbits shown in the figure are as perfect as some 
that have been obtained by accident on other plates. It is 
very difficult to make a plate showing all three forms with 
only four or five trials, as the velocity has to be nicely adjusted ; 
consequently, the curves shown in the figure must not be taken 
as samples of the best that can be produced by a large number 
of trials. 
