1902.] Harmonic Tidal Constants for certain Ports. 91 



take place, and perhaps also a redistribution of the stress due to the 

 applied load. This alteration in the distribution of the internal 

 stresses must be such as to cause the surrounding strong layers to 

 stretch elastically as far as the weak material has been permanently 

 stretched. The alteration in the internal stresses will remain after 

 the applied load is removed, as the material which has been perma- 

 nently deformed will be unable to relieve the stronger material. The 

 apparent permanent set which is shown with quenched material after 

 the removal of applied load, may thus be due to the real permanent 

 exten: ion only of the weak layers, and to the elastic extension of the 

 strong layers produced by the new distribution of internal stresses. 

 This explanation, however, does not suffice, at least in the case of 

 iron and steel, to explain the behaviour of a quenched rod under 

 applied stress, for Diagrams 2 and 3 show that such a rod may be 

 stretched further than is compatible with elastic extension- — even 

 supposing some of the iron to have been overstrained to the maximum 

 in the most favourable direction, without stretching nearly far enough 

 for the yield-point of the iron to have been passed. Hence in the case 

 of iron and steel recourse must be had to the explanations which 

 simply attribute the obseived effects to the formation of alio tropic 

 modifications of the metal or to the changes caused by the transition 

 of the carbon — always present — from one condition to another. 



In conclusion, it may be recorded that pieces of the iron and steel 

 specimens used in this research were polished, etched, and examined 

 under the microscope. In the case of the steel specimens the change 

 from the ferrite and pearlite structure shown with the annealed mate- 

 rial to the martensite structure shown with the quenched steel was 

 very striking. But in the case of the Lowmoor iron no difference 

 was detected by the microscope in the structures of the annealed and 

 of the quenched specimens, although, as shown by Diagram 3, the 

 elastic properties in the two conditions were vastly different. 



" Harmonic Tidal Constants for certain Australian and Chinese 

 Ports." By Thomas Wright, of the Nautical Almanac 

 Office. Communicated by Professor G. H. Darwin, F.RS. 

 Pieceived August 1, 1902. 



Ballina (New South Wates), Princess Royal Harbour (King George's 

 Sound), Newcastle (New South Wales), Brisbane (Queensland), and 

 Sydney (New South Wales). 



The tidal observations made at these five ports have been reduced 

 by the aid of certain sums placed at my service by the Government 

 Grant Committee of the Royal Society, and I am indebted to Professor 



