274 TRANSACTIONS OF SECTION G. 



Of British merchant vessels, 2,700 have been fitted, but, owing to less 

 accurate reports being obtained from merchant vessels as compared with war- 

 ships, the actual results are not known. If, in comparison with British 

 warships, only one-tenth as many merchant vessels, as compared to the number 

 fitted, have been saved, the saving to the country in tonnage has probably been 

 much in excess of one hundred million sterling. 



3. The Thermal Conductivit ij of Solid Insulators. 

 By Professor W. M. Thornton, JD.Sc., D.Eng.' 



Thermal conductivity of metals has been ade((uate!y explained by the 

 electron theory of matter. In the case of insulators the argument does not hold, 

 and the mode of conduction in substances such as quartz or wax has not been 

 worked out. There is a simple relation between the coefficient of therrnal 

 conductivity k, the density p, and the velocity of sound V, in a solid which 

 throws much light on the process. It is that A- = VV. and since V^ = E/p, 

 where E is the elasticity, k='Ep. These relations hold for all true solid in- 

 sulators, but not for indiarubber or cork which have peculiar elastic properties. 



For example : 



Velocity 



of soviiid. 



4-1.105 



4-65 



0-13 



From the kinetic energy of vibration ^7nv" it is found that the ratio of the 

 velocity of sound to the "velocity of atomic vibration by which heat is trans- 

 mitted in insulators is 2-9.10"'. ' It is shown that the coincidence of this with 

 V can be explained and a reason given for the rule /• = V-p'- by simple electro- 

 magnetic considerations. The rule is a useful test for a heat insulator; the 

 chief qualification is that it should be light and inelastic. 



4. The AfpUcaiion of Aerofoil Theory to the Heating of Buildings. 

 By Professor G. H. Bryan, F.R.S. 



The author showed some experiments illustrating by means of smoke the 

 deflection into the room of the upward current of heated air from a radiator 

 placed below a window by means of an inclined plate, the layer of cold air 

 in contact with the window remaining relatively stationary. 



In the afternoon a Sectional Visit was paid to the Winton Aerodrome of 

 the Bournemouth Aviation Company. 



3 See P/nl. Mag., .38, p. 705. 1919. 



