170 Mk. J. Betce oti the Recent Progress of the 



at the greatest heights in no way varied in its proportion of oxygen 

 and nitrogen from its state at the surface ; it did not vary in com- 

 position in the four ascents more than if collected at various points on 

 the surface. The lowest observed temperature was about 11° F. below 

 zero. Reasoning from these observations it maj'^ be concluded, according 

 to Sir John Herschel, that at the top of the atmosphere over the 

 equator, tlie temperature may be taken at ■ — 77^°, and over the pole at 

 — 119^°, supposing the surface temperatures to be respectively 82° F., 

 and 0°"f. 



(11.) With regard to the temperature of the celestial spaces, I am 

 not able to find that anything has been recently added to what has 

 been left us by Fourier, except some late speculations of Mr. Hopkins 

 of Cambridge. Fourier placed the temperature of space somewhere 

 about — 60° F., but has, I believe, left no memorandum of the reasoning 

 by which he was led to this conclusion. We know that the earth has 

 either a fluid nucleus, or concentric fluid layers at an inconsiderable 

 depth ; that of about 10,000 feet, or two miles, would give us the 

 temperature of boiling water ; the increase downward would soon become 

 so great, that at a depth of twenty -four miles, we should meet with 

 a temperature equal that at which iron melts, or 2,786° F. — a heat suf- 

 ficient to fuse all known substances. Below this there may be a solid 

 nucleus ; the melted matter being arranged in concentric spheroidal 

 layers.* Upon any hypothesis we may adopt, conduction and dissipation 

 must be going on ; but the passage of heat is so slow through stoney 

 substances that the internal heat now annually dissipated is thought 

 not greater than rrth of 1° F., or such as would in one year melt Ath 

 of an inch of ice. The earth has arrived at this stationary condition. 

 This heat is dissipated in space, and the radiation of the solar heat 

 received is also constantly going on, but at what rate we are without 

 exact data to fix. The stars and planets may also radiate heat into the 

 planetary spaces, which may, by the combined causes, have some proper 

 temperature of their own. In a late paper read to the Cambridge 

 Philosophical Society, of which I have seen an abstract only, Mr. 

 Hopkins, by a process of reasoning into which I cannot now enter, 

 attempts to show that a minimum temperature exists within the earth's 



* Such is the estimate hitherto formed. A different one, however, has been verj- 

 recently made by Mr. Hopkins. From reasonings founded upon the results of the " Experi- 

 mental Researches on the Conductive Powers of "Various Substances," undertaken by re- 

 quest, and at the expense of, the British Association, he draws the conclusion that the rate 

 of increase of temperature downwards has been taken too great, and that the solid crust is 

 not so thin as geologists have hitherto supposed.— (Abstract of Paper read to Royal Society, 

 in Philosophical Magnzine, April, 1858). 



