458 



R. W. Willson — Magnetic Field in 



The observations upon the magnetic declination at various 

 levels in the elevator shaft, described on page 90, were origi- 

 nally made in order to see if any considerable amount of free 

 magnetism was present in the walls of the central tower. 

 The results showed a far greater effect due to the steam-pipes 

 than any that could be ascribed to the brick-work, and it was 

 this which first led to a careful examination of the pipes and a 

 just estimation of their effect upon the magnetic field. These 

 results are here noted to explain why the very considerable 





a- -, -, 



vZmk a, m ii » ^ 



Fig. 5. Plan of west wing of Jefferson Physical Laboratory, with lines showing 

 disturbances of the earth's directive force due to causes other than presence of 

 steam-pipes shown at A, B, C and F. 



K. Soap-stone sink. 



Scale sixteen feet to the inch. 



