A NEW CUKEENT WEIGHER, ETC. 



483 



portions which project are thus half-cylinders : they have axial grooves into which the 

 leads are soldered. 



After winding the coils the traces of fourteen axial planes at equal angular distances 

 apart were marked on the end faces of each fixed and of each suspended cylinder and on 

 the ungrooved portions of the outer cylindrical surfaces. A number of holes for the 

 fixing of spirit levels and sighting pieces were also drilled. 



TABLE I. Observations for Axial Length of Coils on Suspended Cylinder No. 1. 



Temperature = 15 '50. 



The turning of the marble cylinders was very ably done by Mr. TAYLEBSON, of the 

 Engineering Department of the National Physical Laboratory. 



Axial Length of the Coils. The axial length of each helix was computed from a 

 large number of measurements ; some of these were made on the complete helix and 

 others on portions of it. In addition, the mean value was checked by observations on 

 a steel cylinder, on which a fine spiral groove was cut of the same pitch as the coil. 



3 Q 2 



