APPENDIX 



The Normal Circuit Galvanometer, Coil, Compensator, Electrodes, and Keyboard 

 Photographic Recording Lippmann's Capillary Electrometer Special Keys 

 Units of Resistance and of Conductance. 



IN a physiological laboratory the galvanometer may be used either 

 for special electro-physiological research, or in the course of research 

 work where electro-physiology is of secondary interest the galvano- 

 meter playing the part of a balance, to indicate physico-chemical 

 differences between any two different points. 



The following remarks are more especially directed to meet this 

 latter case. The galvanometer may be looked upon either as a 

 manometer, measuring electrical pressures just as one measures 

 blood-pressure, or as a chemical balance, by means of which one 

 can compare numerically the energy values of physiological pheno- 

 mena capable of an electrical expression. In many cases it will be 

 found convenient, or even necessary, to record the indications of 

 the galvanometer photographically. 



The requisite apparatus consist of: (I) the galvanometer; (II) 

 the compensator ; to these must be added various accessories ; (III) 

 the exciting apparatus ; (IV) the electrodes ; and (V) the keyboard, 

 by means of which the constituent pieces of apparatus will be con- 

 nected together to form what may be termed the normal circuit. 

 (The arrangement for taking photographic records is a further 

 accessory described below, p. 156.) 



The galvanometer. The style of instrument matters very little 

 so long as its sensibility can easily be ascertained and adjusted. 



The delicacy of the galvanometer should be such that o.ooi volt 

 through a megohm gives a deflection of 10 cms. at a distance of 

 2 metres. Thus a deflection of i cm. corresponds in such a circuit 

 to a current of xo" 10 ampere, 



