-1859] WRITINGS OF JOSEPH HENRY. 141 



her progenitor — astrology, yet in this instance, modern 

 science has shown that the stars have really a physical in- 

 fluence upon our earth and on every other planet of our 

 system. If from any point in space a line be extended in 

 thought in any direction, it will ultimately meet a radiating 

 body; and hence every point in space must be constantly 

 traversed from all directions with radiating impulses which 

 give it a definite and fixed temperature. For example, our 

 sun sends a ray to every point of the universe, and every 

 other sun sends a ray to the same point, and the sum of all 

 these rays will constitute the temperature of that point. We 

 say the temperature of that point, by which we mean the 

 effect which would be produced on a thermometer if put in 

 that place ; not that there is any temperature in celestial space, 

 for this, as we have seen, belongs to gross matter, and is pro- 

 duced by the motion of its atoms. The term however is 

 convenient, and we shall continue to use it. 



If the radiating power of the suns remained without 

 change, then the temperature of each point in space would 

 be unchangeable. From this consideration it follows that 

 the planetary space in which our earth is moving has in one 

 sense a fixed temperature (independent of the heat of the 

 sun,) derived from all the other suns of the universe; and 

 this temperature, as we shall hereafter see, has a marked in- 

 fluence on the temperature of the globe. 



We shall return to this subject again, and at present shall 

 merely state that at the polar regions of our earth during 

 the months of winter, the space immediately contiguous to 

 the surface is screened from the heat of the sun, and con- 

 sequently the earth by its radiation, must fall in tempera- 

 ture nearly to that of celestial space. A similar screening 

 takes place in succession on all parts of the earth's sur- 

 face during the night ; and as the loss of heat by radiation 

 depends (as we shall see) upon the temperature of the space 

 into which the rays are sent, every part of the earth's sur- 

 face must be affected more or less by the temperature of inter- 

 planetary space; and if this were to vary, though our sun 

 might continue constant in its emanation, the average ter- 

 restrial temperature would be subject to a change. 



