47Ó 



filling of' the core with a substance of higher permeability might be 

 made to compensate the distribution of the Held above described. 

 In our case however this very topography of the field is desired ; 

 for it is within the peritoneum only and not in the surrounding 

 layer (the thicltness of which individually varies from 2 cm. to JO cm. 

 and even more) that an attraction may be usefully exerted. Towards 

 its other end the core gradually becomes thicker and the end is 

 formed by a flange in order to deci-ease the magnetic reluctance; 

 the counter-action of this pole compared with the attraction of the 

 worliing pole is negligeable. 



The coils are wound with enamelled copper wire or with oxydized 

 square aluminium wire the thickness of which increases by steps 

 from the working pole towards tlie other end. This principle is 

 well-known for galvanometers and has also found partial application 

 in my semicircular magnets. The increased efticiency of the "polar 

 windings" must necessarily cause a greater heating effect which may be 

 counter-acted by water circulation. 



Until now this precaution proved unnecessary, (he more so because 

 too cold iron may cause undesirable vasomotoric reflexes of the 

 patient. The front flange of the coils is conical, in order not to be 

 in the way of the operator's eyes and hands ; it may be provided 

 with a corrugated peripheric radiator. The use of alternating currents 

 is not advisable; but a pulsating cun-ent may be caused by periodic 

 short-circuiting of the magnet, while a non-inductive resistance remains 

 switched in the circuit. The relaxation-lime is a few seconds; by 

 exciting the polar coil only it may be diminished to a few tenths 

 of a second ; when pulsations are often to be applied, it is advisable 

 to use a subdivided core. 



In order to reduce the weight as much as possible the core ought 

 to be saturated only to ^/^ or '/s- A minimum total weight is 

 obtained for a dimensional ratio \) between 3 and 4; then the power 

 required is only little above its minimum value; it amounts at most 

 to 4 K.-watt, for most operations it is considerably less; and con- 

 sidering the short duration of an operation the energy consumed 

 CK, -watt-hours) is but very small. The magnet weighs about 100 kg. 

 and is suspended by a kind of crane above the operation table, in 

 such a way that its 6 degrees of freedom may be disposed, of, i. e. 

 a displacement along the vertical and a rotation around it, and the 

 same for two horizontal axes parallel to the body of the patient 

 and normal to it. Below the patient the RöNTOEN-tube is placed, as 



1) Calculated from the demagnetizing factors for short cores, as measured by 

 S. P. Thompson and E. W. iMoss, Pioc. Phys. Soc. Lond. 21, p. 622, 1909. 



