166 ANNUAL OF SCIENTIFIC DISCOVERY. 



high temperature will bear a less proportion to the total radiation of that 

 temperature than at a low, the consequence will be, that the radiation of 

 single particles will increase with the temperature in a less degree than Du- 

 long and Petit's law would indicate. It may even be that the radiation of a 

 particle of very thin plate may be proportional to the absolute temperature 

 of that particle. Taking a piece of glass or mica, therefore, at a low temper- 

 ature, as it is very opaque with regard to the heat radiated by itself, we may 

 suppose that the total radiation consists of that of the outer layer of particles 

 only, that from the inner layers being all stopped by the outer. At high tem- 

 peratures, however, we may suppose there is not only the radiation of the 

 outer layer, but also part of that of the inner layer which has been able to 

 pass, swelling up the total radiation to what it appears in Dulong and Petit's 

 experiments. This way of looking at radiation may possibly bring the 

 radiative power of particles to obey the same laws with the conducting 

 power of particles, which Professor Forbes has shown decreases with an 

 increase of temperature. 



ON THE HEATING OF THE ATMOSPHERE BY CONTACT WITH THE 



EARTH'S SURFACE. 



The following is an abstract of a paper on the above subject, read before 

 the British Association for 18">8, by Prof. Ilcnne-'sy : 



The temperature of the atmosphere depends principally on the heat which 

 it receives from the sun and on what it loses by radiation. A portion of the 

 solar heat is absorbed in passing through the air, while another portion pen- 

 etrates to the earth's surface. The ground becomes thus heated, and the 

 lower strata of the atmosphere acquire the greater part of their heat from 

 contact with the wanned surface. Ir is admitted that the mode in which the 

 air becomes heated by contact with the ground must be a kind of circulation 

 analogous to that seen in the movements of a heated mass of liquid, such as 

 boiling water. When studying the vertical movements of the atmosphere, 

 he had been led to consider the connection between such movements and the 

 influence of the heated ground. In order to experimentally study the ques- 

 tion, thermometers were suspended at different heights above the ground, 

 and under different circumstances of exposure to the influence of the sup- 

 posed currents. Observations were made every minute, and sometimes every 

 half minute, during short intervals, about the middle of the month of May, 

 on days when the sky was clear, and during which there was consequently a 

 great deal of solar radiation. In general the thermometers exhibited fluc- 

 tuations of temperature, the intensity of which diminished the more they 

 Avere protected from the influence of circulating currents in the air. The 

 greatest fluctuations were presented by thermometers with blackened bulbs 

 exposed in the sun. This arose from the circumstance that the blackened 

 bulbs, by acquiring a high temperature, became themselves disturbing agents 

 in the calorific conditions of the surrounding air. Evidence of similar phe- 

 nomena appears to be presented by the curves of temperature obtained by 

 the aid of photographical registration at the Radcliffe Observatory in Ox- 

 ford. Attention has been called by Mr. Johnson to a remarkable serration 

 in the temperature curves during the day. This serration is found only when 

 there is a considerable amount of solar radiation; it disappears during sun- 

 less and cloudy weather. ^Yhile it is explained by referring it to the influ- 



