116 Rev. Mr Scoresby on the Umform Permeahility 



With these magnets the following experiments, shewing their 

 influence through solid substances, were made. 



Near the engine-house of the Liverpool and Manchester Rail- 

 way, I found a very favourable position for trying the effect of 

 the magnetic influence on the compass, through a solid mass of 

 freestone rock in situ. In the place referred to, the rock is ex- 

 cavated in two parallel positions to a considerable depth into the 

 solid. Between the two is a solid septum 31 feet 5 inches in 

 thickness. The magnets being placed on the one side, and the 

 compass on the other, the position of the needle, (which happen- 

 ed to be so nearly parallel to the wall as to require no directing 

 magnet), was observed, and then the opposite poles of the mag- 

 net were presented, which occasioned a deviation of about ^ of 

 a degree. The experiment was repeated several times with a 

 very uniform result, affording a mean deviation, being the sum 

 of the action of the north and south poles, of about 20' of a de- 

 gree, whilst the calculated deviation corresponding with the total 

 distance of 32 feet 1 inch, viz. 31 feet 5 inches of rock, and 8 

 inches, the distance of the centre of the compass from the rock, 

 was ir. W 



On a subsequent occasion, I attempted to transmit the mag- 

 netic influence through about 60 feet of rock near the same place 

 as that of the above experiment ; but the quantity of " live- 

 iron *^ on the spot, consisting of locomotive engines perpetual- 

 ly passing to and fro, produced such frequent changes on the 

 compass as to defeat my object in this experiment. In conse- 

 quence of this disappointment, I sought in my own premises for 

 a situation suited for my purpose, which the sloping nature of 

 the ground in front of the house readily presented. Placing the 

 magnets in the front garden, and the compass within the house 

 in a cellar kitchen, the magnetic influence had to pass obliquely 

 through an extent of soil, stones, and brick-walls, of no less 

 than 61 feet, in order to act on the compass. But even at this, 

 distance its influence was very perceptible. The mean of six 

 experiments indicated a deviation under the action of the oppo- 



• The proximity of stationary iron has no injurious influence on experi- 

 ments of this kind whatever ; but iron in motion, if sufficiently near to act 

 upon the compass, must necessarily produce an unequal influence. 



