NATURE 



[February 7, 1895 



du _ du dv _ dx' 

 dn do' dn ^" 



du 



= 5-=—, 



"F(x, y, z, t) 



.(7) 



where ^ is the temperature gra iient inwards from the surface, 

 and Co is the value of < at the surface. 



If c'andi( are on^tant everywhere, «ay Cj and /•(!> let us call 

 the surface gradient i:^ : then SlS u = c„v ^ C 



i = I "• ~ v±, 



for the same place at the same time after cooling began. 

 As an example, let 



k = kjiflv + I), 

 and 



^ = ./..:■+ I), 



and measure v on the CeniigraHe scale, c„ andX'^ are the actual 

 capacities and conductivities at o*^ C. , 



II = t-,(i<K^ + •< + C), 



_ ia»,- + I'l _ 



iac, + I. 



Thus if ^ and <(' increase ; per cent, per lOo degrees Cenii 

 grade, and iff, = 4000, as 



a = xo'-'s. K = L + I. 



In the cooling of Lord Kelvin's infinite mas; with a plane 

 face the time which elapses until a pariicul.ir STirfice grail ient 

 is reached is inversely proportional to the s piare of thegraHjeni. 

 If the lime tak»n on the assamption of constant <" and k be 

 called /„, and if the time taken on the assumption that c an I <■ 

 increase ; per cent, for 100 degrees is /, then 



//'. 



Suppose 

 then 



s = so, 

 ///,, = 121. 



So that Lord Kelvin's age of the Earth would be muliiplied 

 by 121. 



It mu^t be understood that my conclusions (KATtJRE, January 

 3i p. 224) are really independent of whether R. Weber's results 

 are correct or not. Lord Kelvin has to prove the impo'sihiliiy of 

 the rocks inside ihe ?arth tieini; better conductors (including con- 

 veclive conduction in case of liquid rock in crevices) than the 

 surface rocks. If, however, Weber's results, as quoted by me, 

 are trustworthy, the above solution is what I take Luid Kelvin to 

 refer to in Ihe first paragraph of his publi-hed letter. In con- 

 sidering all such measurements as those of K. Weber, it must he 

 remembered Ihat the rocks at twenty miiesdeep ate not merely 

 at a hit-h li-mperalure, but also under great pressure. 



January 30. John Perry. 



Oceanic Temperatures at Different Depths. 



Thk que«tion of the pcrsislcnce or otherwise of the tempera- 

 tare of diflTcrcnt strata o( water beneath the surface of the 

 oceans, is one upon which so few observations have been made, 

 thai it will probably be imcesling to students of oceanic phe- 

 nomena 10 publish in NAitni. the results obtained at one spot 

 in the Atlantic, at periods extending over as much as twenty- 

 one years. 



At a position about 200 miles west south-west from Cipe 

 Palmas, in Africa, where the depth of water is about 2500 

 fathoms, and where on the surface the Guinea current is run- 

 ning 10 the eastward, the Chalhn^ r in 1873 and 1876, the 

 lliucanitr in 18S6, and the H'a/enviU/i in 1894, have all 

 obtained serial temperatures ; the firjt three to a depth of 200 

 fathoms, Ihe last 10 150 fathoms. 



The result is given in ihe following table, and illustrated by 

 the diagram. 



NO. 13 19. VOL. 5 1] 



Coiiif arisen pf Ouaii Ttmpiratures ohiaiiicd at Different TimeF 

 in or near the same position, viz. 5 48' jV., 14° zo' IV. 



Bticcanet'r 



Depth in ChatlcMger I CiaUr«gtr I 



r-iihnm^ lemprrtliires, temperatures,' tcmperalures, 



S2S 



796 



69-0 



65-9 

 608 

 5SS 



561 



temperatures, 



22/9/94. 



Soo 

 780 



752 

 69-2 

 62-8 

 602 



58-8 



570 



490 



li.^cad Positions and Observation Spot. 

 Challenger, 



20 40 60 80 100 120 140 160 180 20» 



Diagram shuwiiig temperature at different depths obtained at variout epochs 

 ta I.at. 5 48' N., Long. 14" 20' W. 



It will be observed that Ihe tcnpcratures at the surface vary 

 by 6 '3 1". ; at a depth of 20 (allioins. by 9 '6; at 40 fathoms. 



