162 



times that of the reversing thermometer. Their energy requirements are in 

 these ratios. 



As a corollary to this principle, vacuum tubes have little place in most 

 oceanographic instruments. Their fields of application are those, like radio 

 and acoustics, where ample driving power is not available in the medium. In 

 oceanography, the ideal of "less than one vacuum tube" can still be approached. 



In the discussion that followed Kelvin's paper, the lead pencil apparently 

 came in for further derogatory comment. The Secretary exercised considera- 

 ble editorial discretion, but by reading between the lines, one can see that some 

 of the gentlemen present were convinced that the fountain pen had rendered the 

 pencil obsolete. 



To move the pencil, Kelvin had designed a carriage, moving on a pair of 

 ways, and drawn directly by the wire leading from the float. Apparently, some- 

 one doubted the precision of the instrument, which was on exhibit, and suggested 

 a more complicated method of doing this, for Kelvin remarked, "that good work- 

 manship was too often put into requisition to overcome the evils of a poor de- 

 sign. A good design in many cases required no fitting; and where it was possi- 

 ble, it was better to manage with no fitting; for the finest fitting might be undone 

 by a little warp in the material or by a piece of grit He would test the in- 

 strument by shaking it roughly, and it would be seen that there was no error in 

 the marking. " 



This, it seems to me, may be called Kelvin's Second Law of Oceano- 

 graphic Instrumientation: The instrument should not be dependent on lapped 

 bearings or other precision parts for its operation. 



REFERENCES: J.B. Hersey 

 BERANCK, LEO L. 1949. "Aeoustlc Measurements", Wiley, New York. 



COLE, ROBERT H. 1948. "Underwater Explosions". Princeton Univ. Press. 

 Princeton . 



KOENIG. WALTER and others. 1946. JASA 18 19-49. 



REFEREIVCES; H. Nash 



HOLT, LEE E,. "The German use of Sonic Listening". JASA 19.4. 678-681 July 1947 



URICK, R.J. "Some Directional Properties of Deep-water Ambient Nolse". 

 NRL report 3796, Jan. 16, 1951. 



