508 Mr. R. Phillips on the MagJieiism of Steam. 



from east and west; also one end came to \ inch of the shield 

 opposite to the lower needle of the galvanoscope. This piece 

 of a gun-barrel had been mnde red-hot and slowly cooled, 

 and its magnetism when in the above position was nearly 

 = 0; the diameter of its external surface at that end which 

 was placed in the coil, in this and the following experiments, 

 was about one inch, and this end was made of iron about —^ 

 inch thick, the other end being thinner. There was a distance 

 of about ^ inch between the nearest upper or lower part of 

 the iron and the respective inside surfaces of the coil. 



21. The steam being at 40 lbs. per inch, and the gun- barrel 

 in the coil, five puffs of steam, each puff acting during every 

 alternate vibration of the needles, produced a swing of about 

 25° of the micrometer ; the gun-barrel was now removed, when 

 five puffs of steam, acting as before, produced a vibration of 

 only 10°. This was done many times, and always with the 

 same result. I think better results would have been obtained 

 at a lower pressure than 40 lbs. ; for on examining the vibra- 

 tion at various pressures, the iron being in the coil, I found 

 that a considerable swing was produced almost as soon as the 

 water began to boil at the atmospheric pressure; and shortly 

 afterwards, as the pressure rose, the vibrations became very 

 strong, much stronger than at 40 lbs. The point of the needle 

 moved towards A when the steam was turned on. 



22. During these last experiments, I ascertained that the 

 first puff of steam which passed through the coil when it was 

 cold produced a much greater effect on the galvanoscope than 

 any immediately succeeding puff. This was guarded against 

 by letting off the first puff, then checking the motion of the 

 needles by some inverse puffs, and then proceeding to make 

 the vibration which was to be compared (21.). 



23. I next endeavoured to find the cause of the strong 

 action of the first puff. 



24. The jet and pewter coil (14.), instead of being affixed 

 to the boiler, were attached to a copper box, which inclosed 

 about ninety cubic inches, and the shield and galvanoscope 

 adjusted as before (14.) ; air was now pumped into the box 

 until the pressure rose to about 40 lbs. on the inch, and then 

 discharged through the jet as the steam had been. The 

 needles of the galvanoscope were quite unaffected; conse- 

 quently, air of about the same temperature as the surrounding 

 atmosphere cannot act on a magnet like steam. 



25. It now appeared very possible that the increased action 

 produced by the iron arose from its cooling powers ; and also 

 that by further cooling the coil, a more intense action would 

 be obtained. 



26. The apparatus (17.) had the coil partly immersed in 



