(=-96° F.) by Dulong and Petit's law; but adds, that a closer determination has been made by Professor Moulton, using Stefan's law, that radiation is as the /4th power of the temperature, whence results a mean temperature of-31° F.

This extremely rapid loss of heat by radiation, at first sight so improbable as to be almost incredible, may perhaps be to some extent explained by the physical constitution of the moon's surface, which, from a theoretical point of view, does not appear to have received the attention it deserves.

It must, however, be said that the stupendous volume of solar radiation passes off substantially untaxed into space, and what may actually there become of it science is unable to tell.

In this condition there is a tendency to cool by radiation until some critical layer, B, reaches its due point.

A stratus cloud is thus formed at B; from this moment A B continues to cool, but B C is protected from radiating, whilst heated by radiation from snow and possibly by release of latent heat due to cloud formation.

We have been looking up the records to-day and find that Amundsen on a journey to the N. magnetic pole in March encountered temperatures similar in degree and recorded a minimum of 79°; but he was with Esquimaux who built him an igloo shelter nightly; he had a good measure of daylight; the temperatures given are probably 'unscreened' from radiation, and finally, he turned homeward and regained his ship after five days' absence.

I have accordingly constructed an instrument of large dimensions, a polygonal reflector (see Fig. 1), composed of a series of inclined mirrors, and provided with a central heater of conical form, acted upon by the reflected radiation in such a manner that each point of its surface receives an equal amount of radiant heat in a given time.

It should be mentioned that the indications of the thermometer during the experiment have been remarkably prompt, the bulb being subjected to the joint influence of radiation and convection.

But the determination of temperature which uninterrupted solar radiation is capable of transmitting to the polygonal reflector calls for a correct knowledge of atmospheric absorption.

Accordingly, an observation of the temperature produced by solar radiation at a zenith distance whose secant is twice that of the secant of 17° 12', viz., 61° 28', determines the minimum atmospheric absorption at New York.

In other words, the temperature produced by solar radiation is as the density of the rays.

It will be remembered that Sir Isaac Newton, in estimating the temperature to which the comet of 1680 was subjected when nearest to the sun, based his calculations on the result of his practical observations that the maximum temperature produced by solar radiation was one-third of that of boiling water.

This practical demonstration, however, has been questioned on the insufficient ground that "the eccentricity of the earth's orbit is too small and the temperature produced by solar radiation too low" to furnish a safe basis for computations of solar temperature.

With reference to the "low" solar temperature pointed out, it will be perceived that the adopted expedient of increasing the density of the rays without raising the temperature by converging radiation, removes the objection urged.

It will be noticed that the temperature of the large heater is proportionally higher than that of the small heater, a fact showing that the latter, owing to its higher temperature, loses more heat by radiation and convection than the former.

F. It is hardly necessary to observe that this temperature (developed by solar radiation diffused fully ten-thousandfold) must be regarded as an actual temperature, since a perfectly transparent atmosphere, and a reflector capable of transmitting the whole energy of the sun's rays to the heater, would produce the same.

The sense of perfect health came to hima steady, rhythmic radiation; not a tired, weak fibre, but a singing vitality of every tissue, as if it were cushioned in some life-giving fluida pure perfumed bloom of health.

The most remarkable and, at first sight, astounding thing about this furnace is, however, that it works solely by radiation.

Yet so it turns out, not by warming solid objects or by dull warm surfaces, but by the brilliant radiation of the hottest flame that can be procured, will rooms be warmed in the future.

And if one wants to boil a kettle, it will be done, not by putting it into a non-luminous flame, and so interfering with the combustion, but by holding it near to a freely burning regenerated flame, and using the radiation only.

Hence, between a flame and the surface to be heated by it there always intervenes a comparatively cool space, across which heat must pass by radiation.

It is by radiation ultimately, therefore, that all bodies get heated.

The second condition of radiation was high temperature.

Whether this be so or not, his radiating flames are most successful, and the fact that large quantities of steel are now melted by mere flame radiation speaks well for the correctness of the theory upon which his practice has been based.

"Regenerative Furnaces with Radiation," and "On Producers," by F. Siemens; Journal Soc.