Finally, comparative observations made simultaneously on the borders of the lake, within a few feet of the water, gave the following result: —
| Temperature of the surface of the gravel | 9.90 C. |
| Temperature of the air 3 inches above the ground | 10.40 |
| „ „ 6 feet „ | 10.55 |
| „ „ 15 feet „ | 10.62 |
showing that the immediate neighbourhood of the water is sufficient to modify the results generally obtained on land.
The following conclusions may, I think, be safely drawn from the foregoing observations: —
1. The gradual increase of temperature occurring on ascending through the lower strata of the atmosphere, which appears constantly to prevail on land about and after sunset, is not apparent above a large surface of water.
2. The immediate vicinity of a large sheet of water is sufficient to modify to a considerable extent the effects of the nocturnal radiation of the earth, and thereby materially diminish the increase of temperature observed under ordinary circumstances on ascending above the surface of the ground.
3. One cannot help being struck by the great difference (amounting to between 2 and 3 Centigrade degrees) constantly observed between the temperature of the atmosphere a few feet above the ground, and that of the air at the same height above a large sheet of water.
III. On Physical Lines of Force. By J. C. Maxwell, F.R.S., Professor of Natural Philosophy in King's College, London[1].
Part III. — The Theory of Molecular Vortices applied to Statical Electricity.
IN the first part of this paper[2] I have shown how the forces acting between magnets, electric currents, and matter capable of magnetic induction may be accounted for on the hypothesis of the magnetic field being occupied with innumerable vortices of revolving matter, their axes coinciding with the direction of the magnetic force at every point of the field.
The centrifugal force of these vortices produces pressures distributed in such a way that the final effect is a force identical in direction and magnitude with that which we observe.
In the second part[3] I described the mechanism by which these rotations may be made to coexist, and to be distributed according to the known laws of magnetic lines of force.
