473 



The attraction of a number of test-spheres or pills was measured 

 under different circumstances with a spring-balance; its maximum 

 was found at a distance of 4 — 5 cm. and amounts up to 25-fold 

 weight; the greatest "carrying distance" is 22 cm., for test cylinders 

 even more. For a round drawing-pole the maximum was found at 

 2 or 3 cm. and reaches 50-fold weight; at distances greater than 

 7 cm. the attraction becomes smaller than that observed without 

 the use of a pole-shoe. The coils were constructed in such a way 

 that their purely electrodynamic attraction, which is determined by 

 the square of the current, contributes considerably to the total force. 

 With a d ragging-pole a transverse force is obtained up to 25-fold 

 weight at a distance of 2,5 cm. 



Though for our purpose the type described proved amply sufficient, 

 it appears however interesting to study the properties of a similarly 

 enlarged or reduced instrument. If the linear dimensions be n-iold 

 the weight of the iron varies as n\ that of the copper as 7i^ (or as 

 n^, depending on the mode of winding), t'^e kilowatts consumed as 

 n (or respectively as if), the attraction of non-saturated particles at 

 a given distance however nearly as n\ This 4''^ power (in fact 

 about the 3,7^'^) is evidently very favourable, especially as compared 

 with the above-mentioned very uneconomical logarithmic progression 

 for field-magnets. We may safely predict that it will be possible to 

 produce any necessary force with magnets which do not yet become 

 unmanageable and the cost of which will hardly prove a serious 

 obstacle in this case, where life and health of the patients may be 

 at stake. 



Exti^acting magnets. In this way it ought to be possible to move 

 about ferromagnetic probes brought into the body on purpose or to 

 extract undesirable objects, such as steel bullet shells, broken needles 

 or injection-syringes and various iron or nickel objects, which are 

 daily met with in the surgery of accidents. 



Also an effect on other organs, less soft than the intestines may 

 be thought of. It has long been known that all tissues are diamagnetic; 

 Faraday already showed that this is also the case with blood ; the 

 iron atoms in haemoglobine are bound in such a way that no para- 

 magnetism occurs, no more than e.g. for potassium ferrocyanide. 

 PLtJCKER ^) showed that a magnet repels the red blood globules 

 relatively to the serum. It is moreover also known that the flow of 

 diamagnetic liquids through tubes and their dropping may be con- 



1) A. Plücker, Pogg. Ann. 73 p. 576, 1848. 



