232 Mr. R. Phillips on the Magnetism of Pewter Coils, 



glass catch-tube. A copper pan was brought under the platinum 

 tube, so that the tube could easily be put under water by filling 



i;he copper pan. The pan contained stout wire supports, on 

 which rested a square piece of iron 4*5 inches in each side and 

 j\j inch thick, which had been made red-hot and slowly cooled ; 

 a good bearing for the iron was obtained on three points, and it 

 lay horizontally at a vertical distance of about -^-^ inch from the 

 tinder side of the platinum tube : supposing a perpendicular 



?plane to have been raised from the iron to the nearest line on 

 the platinum tube parallel with its axis, it would have been found 

 that the iron extended | inch in an easterly direction from this 

 plane towards the galvanoscope, at which distance the iron came 

 in contact with one of the flat sides of the pan. The platinum 

 tube was united to the glass tube by India-rubber, oiled silk 

 and thread only ; and the needle of the galvanoscope lay about 

 parallel with, and in the same horizontal plane as, the axis of 

 the platinum tube. 



155. With the steam at about 25 lbs. per inch, five puffs 

 sent the edge of the needle about the whole length of the scale ; 

 and the swing was to A when the steam was turned on. In this 

 way I made many experiments, having the platinum tube some- 

 times partially and sometimes entirely covered with water ; but 

 I could not obseiTe any decided difference, although I think on 

 the whole the magnetism was perhaps rather stronger when the 

 tube was about ^rd immersed ; the tube was always parallel with 

 the surface of the water. The internal diameter of the platinum 

 tube was \ inch, and it was about -^^ inch thick. 

 .. 156. A pewter tube 5 inches long, -^^ inch internal diameter, 

 and -^-Q inch thick was substituted for the platinum tube. When the 

 tube was about one-third covered with water, the swing was just 



^ias with the platinum tube ; but when the tube lay entirely under 

 water, the swing was about one-half less; with this exception 

 everything was as with the platinum tube. 

 , 157. I could produce no effect on the galvanoscope by sub- 



c. ktituting a glass tube, nor with the metal tubes when the iron 

 was away, nor when the iron was in its place unless the tubes 



^were kept cool by water. 



_/ 158. The variation in the magnetic intensity of the pewter 



^ tube led me to suppose that the direction of the magnetism of a 

 coil would vary according as cold was applied to it. A pewter 

 pipe 3 feet 8 inches long, \ inch internal diameter, and -^-q inch 

 ijhick, was wound up into a helix ; the convolutions lay regularly 

 rside by side, but without overlapping ; the interior of the coil 



! measured 1*3 inch diameter, and there were six convolutions. A 



^ piece 7 inches long was left unwound at each end of the pewter 

 pipe, and the ends were each furnished with a stop-cock having 



