42 PHYSIOLOGICAL PHYSICS. [Chap. iv. 



obtained. So a current of a few Grove's cells, which 

 might be permitted to pass through the body without 

 the person being aware of any effect, would, if sent 

 through a large coil, be able to generate induced cur- 

 rents sufficient to kill an ox. 



Du Bois-Itcymoiid's iBidiictorium, or in- 

 duction coil, is constructed on similar principles with 

 a view to physiological experiments. The primary 

 coil R 1 , consisting of about 130 turns of a moderately 

 thick insulated copper wire, is fixed, and has 



Fig. 23. Du Bois-Eeyinond's Sledge Inductoriuin. 



a core of soft iron rods. The secondary coil R 2 , 

 having 6,000 turns of thin (0-15 mm. in section) 

 copper wire, is quite separate, and slides in a groove 

 B along the wooden ways BB. These ways are made 

 double, and hinged, so that they can be folded back, 

 or unfolded, when a grooved roadway is obtained 

 twice the length shown in the figure, along which R 2 

 may slide. Thus R 2 may be brought quite over R 1 , or 

 may be moved away to a considerable distance. As 

 already noted (page 39), on the distance between the 

 two coils depends the amount of the induced currents. 

 A centimetre-millimetre scale is pasted along the edge 

 of BB, so that the distance between the two coils can 

 be always measured, and consequently the same 

 strength of current at any time reproduced, provided 

 other things, such as element, etc., are equal. 



At the end of the apparatus is the arrangement 

 known as Wagner's hammer, adapted by Neef for 



