The observations in each line of the table apply to a period of twenty-four hours, beginning at 9 A. M. on the day indicated in the first column. A dash denotes that the result is included in the next following observation.

REMARKS.

Fifth Month.-1. Fine. 2, 3. Rainy. 4, 5. Showery. 6-8. Fine. 9. Fine : a solar halo, coloured, a little before sunset. 10. Fine: a lunar halo of the largest diameter. 11. Overcast: cold wind: a lunar halo at night, with a bright spot on each side, at the same height as the moon. 12. Showers. 13. Rainy. 14. Rainy. 15. Rain, without ceasing, all day. 16. Cloudy. In consequence of the heavy rains of the last four days, amounting on the whole to 2.91 inches, a flood was naturally expected this morning; and towards evening the waters rose suddenly in the sea, and passing over all the banks of the level, soon filled the marshes, and in the course of the night rose to an unprecedented height, being 24 inches higher than in the flood of 1809. The houses in the marshes south of the road were filled nearly to the chamber floors, and some of the inmates removed with great difficulty: the flood remained stationary for nearly 24 hours. On the 17th in the afternoon, it began very gradually to subside, and on the 18th, in the morning, was much abated; the marshes still presenting the appearance of a bed, the tops of the trees appearing in places only. 17-19. Cloudy and fine. 20-23. Fine. 24. Morning showery. 25-29. Fine. 30. Fine: a slight shower in the morning.. 31. Cloudy and fine.

RESULTS.

Winds: N, 6; NE, 8; E, 3; SE, 1; SW, 5; NW, 8.

ANNALS

OF

PHILOSOPHY.

AUGUST, 1824.

ARTICLE I.

Remarks on Solar Light and Heat. By Baden Powell, MA. of Oriel College, Oxford, and FRS.

(Continued from vol. vii. p. 406.)

(27.) In the conclusion of a former paper I alluded to some further experiments which were to follow, relative to the question of the proportion obtaining between the heating and illuminating effects of the solar rays. The method of experimenting alluded to is one which I have not been able to apply to any extensive series of different intensities. It consists in compar ing the effect produced on a blackened thermometer by the focal light of different lenses, with the relative calculated intensities of the rays in those foci. Thus we may ascertain whether at these high intensities the same proportion is maintained. Without proof we cannot assume that it is; and a very few comparisons may be sufficient to show, whether the proportion is nearly preserved, or whether there be any considerable deviation from it.

(28.) When thermometers are exposed to the action of radiant matter there are several considerations to be attended to in comparing their observed risings; and it will be convenient in the first instance to bring these considerations into one point of view.

A thermometer exposed to radiant matter absorbs heat only on one-half of its surface, while the other half is radiating again its acquired heat, and the observed effect depends upon the equilibrium which obtains between them. In particular cases only part of one surface may be exposed to heat: the difference between such part and the whole surface, together with the absorbing and radiating powers of the surface, must, therefore, be taken into consideration, as also the rate of communication of heat dependent on the mass.

New Series, VOL. VIII.

G

Let the portion of the surface of the bulb exposed to

The observed rise in a given time

The power of the coating for absorbing heat (of what

ever kind).....

And for radiating it....

The intensity of heating power,.

If in this last case the thermometers be exposed to simple radiant heat, assuming the universality of the law, that the absorptive is proportional to the radiating power of a surface, we shall have

Or hence we might derive a neat and simple method of verifying that law.

1

The relative values of p and k as compared with a surface of glass in particular cases, may be obtained by coating only half

the surface of the bulb, and exposing either the plain or coated side to the same intensity of heat. The ratio may be obtained

k k1

by heating two bulbs completely coated to the same point, and observing their rates of cooling.

The case (C) is the same as that investigated in the Phil. Trans. 1800, No. 19, note, p. 447.

(29.) Comparison of the Focal Effect of Two Lenses on a Thermometer coated with Indian Ink.

In order to proceed to this comparison, we must first observe, that when in the formula we take a . d2, it is on the supposition that parallel rays impinge on a spherical surface. With the focus this is not the case, and from the convergence of the rays, as well as from their greater intensity at the outer edge, we may in this case assume, without fear of error, that a = the area of the section of the rays impinging, and thus apply the formula. Thus we have the following data:

=

From the above experiments, rī 10, 31: it is also r = evident, that p = p, and k = k1. By measurement, the diameters of the focal disks were:

and we have to apply the case of the formula (B)

(30.) In order to calculate the respective intensities of light, or number of rays collected in the focus of each lens, we may easily proceed by the well-known theorem,