178 InteUige7ice and Miscellaneous Articles. 



quire its use at all, as the j)roof of the existence of the needle is our 

 only aim. I have used the horse-shoe magnet, but should prefer, in 

 most cases, an electro-magnet like this, made for me by Messrs. 

 Home of Newgate Street, which is made of a simple straight bar of 

 soft iron, wound round 'with wire. Your chemical lecturer has, 

 doubtlessly, made you aware that the magnetic effect is proportionate 

 to the power of the battery, so that if you were desirous of produ- 

 cing but slight effect, you would employ this tumbler battery ; but if 

 you required the action to be manifested at a greater distance, you 

 would use a compound battery, such as this trough battery upon the 

 table. The compound battery will magnetize a needle, in conjunc- 

 tion with the electro-magnet, in tlie space of two or three minutes. 

 A powerful permanent magnet would answer as well as the tempo- 

 rary magnet ; but it would be very expensive, and not so constantly 

 at hand. When soft iron is impacted in any part of the body, we 

 do not require either the electro- or permanent magnet, for on this 

 substance we are unable to confer magnetic properties. 



" To test the existence of a magnet within the body, we may take 

 a magnetized sewing needle, and suspend it by a inece of silkworm's 

 silk, when it will exhibit certain phsenomena upon the approach of 

 the suspected part, provided it contain a piece of magnetized steel. 

 Although this simple contrivance will amply suffice, I myself pos- 

 sess a needle which was made for me by Messrs. Willats of Cheap- 

 side, and which is well-adapted for the purpose. 



" It consists, as you perceive, of a delicate needle, about six inches 

 long, centred upon a small agate cup, resting uj)on a steel point ; 

 so that the smallest possible amount of resistance is offered to its free 



" When a part containing magnetic steel is brought near the 

 needle, it may be either attracted or repelled, it may move upwards 

 or downwards, or it may exhibit disquietude according to the posi- 

 tion in which the new magnet is held. We may detect the position 

 of the foreign body, when it is of any size, by ascertaining where its 

 north and south poles lie, and these are determined by their repelling 

 and attracting the opposite poles of the magnetic needle. The dis- 

 quietude, or motion upwards and downwards, merely indicates mag- 

 petism, but not the direction of the magnet. 



" You will, doubtless, be surprised when I tell you, that in this 

 manner I have detected a piece of needle impacted in the finger of a 

 young woman, although it weighed but the seventh of a grain. 

 This gave such marked indications, that I found out tolerably well 

 the position of its north and south i)oles, though I could not ascer- 

 tain the presence of a foreign body in any other way.' I tried expe- 

 riments on smaller pieces, at short distances, such as half an incli to 

 an inch, and I found that a piece of needle, weighing l-60th of a 

 grain, gave decided indications after having been magnetized, and 

 perhaps even a still smaller amount of steel might in some cases be 

 detected. 



" I have now satisfactorily demonstrated to you, that magnetism 

 may be used for the detection of steel particles impacted within the 



