30 REPORT—1857. 
If temperature were recorded at every station on the surface of the earth at the 
mean time corresponding to any given meridian, then a line traversing the places 
where such temperatures were found to be equal would be a simultaneous isothermal 
line. The forms of such lines would manifestly depend on the diurnal range cf tem- 
perature at the several stations, as well as the several physical conditions influencing 
mean temperature. If the earth were absolutely at rest, and stripped of its fluid 
coverings, these lines would be circles, having their planes perpendicular to a line 
joining the centres of the earth andsun. This would be nearly the case in a body 
turning very slowly on its axis, like our satellite, in which Prof. Hennessy anticipated 
that observations would ultimately show a great diminution of heat radiated from 
the edges compared to the centre of the illuminated disk. With a more rapid motion 
of rotation, as in the case of the earth, the isothermals would be elongated in a direction 
parallel to that of the rotation. On introducing the influence of all the actual motions 
of the earth, and of the emissive and absorbing powers of the atmosphere, the ground, 
and the sea, the forms of these lines would be considerably modified. The forms of the 
isothermals on the land and sea would necessarily differ, and might be expected to 
present some important relations to the directions of Jand and sea breezes. It 
appears, in general, far more probable that a knowledge of the contemporaneous 
conditions of temperature at different places would assist in pointing to a connexion 
between these phenomena and atmospheric perturbations rather than a knowledge 
of mean temperature. Atmospheric currents, whether vertical or parallel to the 
earth’s surface, depend upon contemporaneous differences of temperature. A similar 
remark might be applied to many other important atmospheric phenomena, and these 
lines would also serve to indicate more clearly, or to lessen the possibility of the 
supposed connexion between terrestrial magnetism and terrestrial temperature. 
On the Distribution of Heat over the Surface of the British Isles. 
By Professor Hennessy, M.R.LA. 
Since the author had communicated to the Section at the Cheltenham Meeting of 
the Association an account of his general views as to the laws of distribution of 
isothermal lines, further confirmation of these views had arisen. It had been already 
shown that the isothermals in Ireland are partly closed curves surrounding a space 
of minimum temperature, having its centre a little to the north-east of the centre of 
the island. With the aid of the observations collected and published by Mr, Glaisher, 
those contained in Prof. Dove’s Reports, and a few additional isolated results, the 
isothermals for Great Britain have been laid down on the map exhibited to the 
Section. No correction has been made for elevation above the sea-level, as atmo- 
spherical phenomena do not depend upon the fictitious temperatures so deduced, but 
upon their actual amounts. This non-reduction would partly account for the remark- 
able decrease in temperature in going from the coast towards the interior of the 
island, and by which the space of minimum temperature in Great Britain appears to 
occupy a position between the midland counties of England and the north of Scot- 
land, where it expands to its greatest breadth. The influence of distance from the 
sea and of height above it are, doubtless, both combined in producing the remarkable 
forms of the isothermals of the British Isles, and it would therefore be desirable in 
future tables of the distribution of temperature to have the former element noted in 
connexion with each station as well as the latter. 
On the Vertical Currents of the Atmosphere. 
By Professor Hennessy, M.R.L.A. 
The anemoscope described by the author at the Cheltenham Meeting of the Asso- 
ciation having been since modified, has enabled him not only to observe the vertical 
direction of atmospheric currents, but also to compare the intensity of the vertical 
with the horizontal force of such currents. This is done by observing the angle of 
inclination of a moveable flange, which is turned by the vertical and horizontal com- 
ponents of the current until it is in equilibrium. By integrating the elements 
these components at each side of the fiange, it was easily shown that the horizontal 
force, multiplied by the tangent of the angle of inclination, would give the vertical 
