RHITMKORP'S COIL.] TJNDULATORY FORCES. ELECTRO-MAGNETISM. 



255 



of administering electricity in rheumatic, paralytic, and 

 other nervous diseases ; in cases of asphyxia, from inhaling 

 carbonic acid gas, drowning, cfcc. The power of the shock 

 may be regulated by the removal from, or gradual intro- 

 duction of, the iron rod into the hollow of the cylinder on 

 which the coil is wound ; by means of which the mag- 

 netic effects of induction are lessened or increased. 

 Another plan, having the same result, is that of inter- 

 posing a column of water between one of the wires of the 

 secondary coil and the handle ; for as the liquid conducts 

 to a much less extent than the metal, the intensity of the 

 shock received is readily proportioned, by the length of 

 the liquid column, to the condition of the patient. 



If one of the wires of the secondary coil be attached to 

 a file, and the other be drawn quickly over its surface, 

 bright sparks will be produced ; and if the ends of the 

 wires are immersed in acid water, or a solution of 

 sulphate of copper, decomposition of the liquid ensues. 

 But both the chemical and luminous effects of the 

 secondary current are very feeble ; its characteristics 

 l>i-iii^ great intensity and the absence of quantity.* 



We have confined our description to one form of the 

 coil machine ; but may observe, that they are made in 

 various ways by the instrument-makers, both as to the 

 arrangement of the coil itself, and the other parts of which 

 it is composed. We shall now proceed to describe a 

 most valuable modification of this instrument, which has 

 been invented by M. Rhumkorf, and by whose name it 

 is generally known in scientific circles. 



RHUMKORFS COIL. 



PBEHAPS one of the most interesting instruments which 

 have been introduced to the notice of the experimental 

 philosopher during the present century, is the coil con- 

 structed by M. Rhumkorf, of Paris, and improved lately 

 by many eminent electricians. It has afforded us a 

 complete connecting link between fractional and voltaic 

 electricity, and so has removed many difficulties which 

 had previously existed between those two branches of 

 electrical science, in respect to their general laws and facts. 



The description we have already given of the ordinary 

 coil machine, will prevent the necessity of describing some 

 portions of M. llhumkorf s instrument. It has a primary 

 and secondary coil, and a contact-breaker, which, how- 

 over, is of a peculiar construction. The principal points 

 of difference between the two machines are, that the 

 Rhumkorf coil has a very great length of secondary 

 wire, extending to many thousand feet it being of 

 extreme fineness; and also a "condenser," which is not 

 found in the common instrument. 



Each layer of the secondary coil is insulated from its 

 neighbour by a thin sheet of gutta-percha, or other non- 

 conducting material. This prevents a great loss of intense 

 electricity, which otherwise would occur. The condenser 

 consists of a large sheet of tinfoil, enclosed in sheets of 

 oiled silk. It is attached to the primary coil ; and has the 

 effect of increasing the intense effects of the secondary 

 coil, by modifying the quantitive nature of the primary 

 one. 



At one end of the instrument two glass upright pillars 

 are placed ; into the top of each of these the terminals of 

 the secondary coil are lixud. From these, wires may be 

 extended, which can be connected with any apparatus to 

 be employed in the course of experiments. 



We may remark, that in all our experiments with 

 Rhumkorfs coil, or its modification, the greatest effect 

 lias been obtained when the contact-breaker has been so 

 regulated as to give a minimum of currents per minute. 

 We have previously remarked, that it requires an appre- 

 ciable interval of time to render a rod of iron magnetic 

 by means of the voltaic current ;t and in the coil of which 

 we are speaking, another element must be considered ; 

 which is, the great length of the secondary coil, and the 

 resistance which it may afford to induction, (tc. 



Four cells of Grove's battery, with platinas, each ex- 

 posing an active surface of sixteen square inches, afford, 

 so far as we have seen, the best effects with tho instru- 

 See anti, p. 2il. * See antt, p. 119. 



ment. Care must be taken not to use too great a 

 battery power, lest the primary coil be heated. This 

 frequently occurs if a large battery be employed with 

 the coil already described;! aQ d it would certainly 

 injure a Rhumkorf arrangement, and perhaps render it 

 useless. In the ordinary coil, the battery is directly 

 connected with it ; but in M. Rhumkorfs apparatus, a 

 commutator is provided, by means of which the current 

 can be turned on and off as required, or be reversed in 

 its direction, which is frequently necessary in some ex- 

 periments. Another advantage is secured, which is of 

 no mean importance. As the handle of the commutator 

 is insulated from the battery and coil, the experimenter 

 runs no risk of receiving any shock. Those who havo 

 accidentally received one from a Rhumkorf, will not 

 easily forget its effects. The writer was twice unfortu- 

 nate in this respect, and suffered for some days after 

 their occurrence. The outside of the coil is as highly 

 charged as the terminals ; and long sparks may be ob- 

 tained from it, just as may be taken from the conductor 

 of an electrical machine. If a wire proceeding from the 

 outer extremity of the secondary coil, or from its external 

 surface, should happen to fall on the table on which the 

 instrument may be standing, a powerful shock is often 

 experienced if the operator touch any part : indeed, it is 

 impossible for us to urge too strongly, that the greatest 

 care be observed in handling the instrument, or in 

 avoiding neglect with respect to the management of the 

 wires proceeding from it. 



Since the first introduction of the Rhunikorf coil, it 

 has undergone numerous modifications, which have con- 

 listed in the extension of the condenser, improved insu- 

 lation of the coils, <tc. A spark of half an inch in length 

 was considered a great achievement ; but we lately 

 observed in a periodical, that M. Rhumkorf had suc- 

 ceeded in obtaining one seventeen inches long, between 

 the terminals of the secondary coil. 



Having thus explained the construction of M. Rhum- 

 korf s coil, and of its modifications, we may suggest a 

 few experiments, which will illustrate some of its pecu- 

 liar powers ; and for this purpose we shall choose such 

 as will show how far it connects the phenomena re- 

 spectively afforded by frictional and voltaic electricity. 

 The following engraving represents a Rhumkorf of tho 

 form usually sold at tho instrument-makers. 

 Fig. 18. 



i-imcnt 12. Having attached the wires of tho 

 battery to the coil at the proper binding-screws, fix, in the 

 two pillars holding the terminal wires of the secondary 

 coil, a platina wire in each, so that their two points may 

 be within |ths of an inch of each other ; turn on tho 

 commutator, and a constant stream of purple-coloured 

 fire will be produced between tho two points. 



Exjieriment 13. It will be noticed that one wire will 

 become red-hot, whilst tho other remains comparatively 

 cool. But reverse the direction of the commutator, 

 and immediately the effects of heat will also be oluuupaa 

 that wire wliich had been previously cool, becoming 

 heated. 



Experiment 14. Separate the two wires to a distance 

 of an inch from each other ; taking care, however, in 

 this, as in all other experiments, that the current from 

 the battery has first been turned off. On again turning- 

 on the primary current, no sparks will pass between tho 

 secondary wires ; but if the ilamo of a spirit-lamp bo 

 placed so that each wire may enter, then tho spark will 

 at once dart through the heated air, although it will not 

 through the atmosphere in its ordinary state. 



See ante, p. 254 ; Fig. 17. 



