210 Mr. T. M. Reade on the Geological Consequences of a 



it to simple algebra. I was led to it by an examination of 

 the effect of telephones bridged across a common circuit (the 

 proper place for intermediate apparatus, removing their im- 

 pedance) on waves transmitted along the circuit. The current 

 is reflected positively, the charge negatively, at a bridge. 

 This is the opposite of what occurs when a resistance is put 

 in the main circuit, which causes positive reflexion of the 

 charge, and negative of the current. Unite the two effects 

 and the reflexion of the wave is destroyed, approximately 

 when the resistance in the main circuit and the bridge re- 

 sistance are finite, perfectly when they are infinitely small, as 

 in a uniform non-distortional circuit. 



XXV. The Geological Consequences of the Discovery of a 

 Level- of -no- Strain in a Cooling Globe. By T. Mellard 

 Reade, C.E., F.G.S., F.R.I.B.A.* 



WHILE working out my theory of the Origin of Moun- 

 tain-Ranges I became clearly convinced that there 

 was a fallacy underlying the popular conception of the effect 

 of secular cooling upon the crust of the earth. It is very ex- 

 traordinary that the physicists who supported the hypothesis 

 that mountain-chains had been ridged up through the outer 

 uncontracting crust following by gravitation the shrinking 

 nucleus, were content to leave the idea in this very vague 

 form. 



It is obvious, when once pointed out, that on this hypo- 

 thesis it is only the actual surface of the earth that does not 

 contract. As the isogeothermal lines sink deeper in the pro- 

 gress of secular refrigeration, each zone below the surface in 

 the solid crust must contract horizontally proportionately to 

 the lowering of the temperature. At a certain depth the rate 

 of this horizontal, or in other words circumferential, contrac- 

 tion must equal the mean rate of the radial contraction of 

 the sphere. At this particular zone — which varies in depth 

 as the time — I showed f that there is no strain ; while all 

 of the crust above it is in compression, and below it all the 

 cooling matter is contracting. After fully realizing this con- 

 ception, a few calculations convinced me that on the hypo- 

 thesis that our globe has cooled in this way during all geolo- 

 gical time, the level-of-no-strain, as Mr. Fisher aptly names 

 it, could not at the present time be many miles deep below 

 the surface. All this seemed so very clear to me that I 



* Communicated by the Author. 



f Chap. xi. ' Origin of Mountain Ranges.' 





