NATURAL PHILOSOPHY. 109 



ward of the compass, the principal mass of the cylinder being below 

 the level of the needle and card, and its upper end being 2 inches 

 above that level. By this means a deflection or deviation of 10 10' 

 was produced, the north end of the needle being drawn that amount 

 to the eastward of the correct magnetic north. Cylinder No. 2 was 

 next placed inside of No. 1, when the deviation was increased to 12 

 15'. Cylinder Xo. 3 was then placed inside of No. 2, and the devia- 

 tion was again increased to 14 15', the north end of the needle being 

 drawn to the eastward in each case. Hansteen's Magnetic Intensity 

 instrument was then placed with the centre of its needle (as nearly as 

 t could adjust it) in a similar position to that which the course of the 

 compass had occupied, and the following results were obtained : 



Time of 100 vibrations, starting from an arc of 18 

 Previous to the cylinders being brought into the observatory, 6' 57" 



No. 1 cylinder in place, & 51" 



No. 2 cylinder in place inside of No. 1, . . . & 47" 

 No. 3 cylinder in place inside of No. 2, . . . .6' 45" 



" The intensity instrument being removed, a dipping needle was 

 then employed, and the following are the results of observations : 



Dip. 



Previous to the cylinders being brought into the observatory, 68 37' 

 No. 1 cylinder placed to the south of the instrument, . 70 10' 

 No. 2 cylinder in place inside of No. 1, . . . 70 27' 

 No. 3 cylinder in place inside of No. 2, . . . . 70 37' 



" The conclusion to be deduced from all these observations appears 

 to be, that to the deduced magnetism of the surfaces of the cylinders 

 acting upon each other is due a portion of the deviation ; and reason- 

 ing by analogy, a similar deduction is applicable to the telescopic fun- 

 nels of steamships." 



INSULATOR FOR WIRES OF THE ELECTRIC TELEGRAPH. 



A PATENT has been obtained by Mr. John M. Batchelder, of Boston, 

 for an improved insulator for wires of the electric telegraph. It con- 

 sists of a cast-iron cap, which is lined throughout with glass by the 

 operation of blowing. The shank, or holder, is then introduced with a 

 hot mass of glass, by which it is firmly fixed in its place in the centre 

 of the cap. The distance from the shank to the lower edge of the cap 

 is about four inches, measured upon the surface of the glass. When 

 the shank is inserted, the end is prevented from coming in contact with 

 the metallic cap by the glass lining ; thus insuring perfect insulation 

 at this point. The wires are attached to the top of the insulator, or at 

 the side, as may be preferred. The reentering angle at the lower part 

 of the cap protects the glass within from missiles, and is calculated, in 

 a storm of wind and rain, to direct the rain downward, and thus pre- 

 serve the insulation. The patent also includes a lining of porcelain, 

 which is applied to the inner surface of the cap, in the same manner 

 as in culinary utensils. This insulator is used for the wires of the 

 Municipal Telegraph, recently introduced in Boston. Editor. 



