ANIMAL AND VEGETABLE 241 



In this way, almost irrespective of the position of the 

 patient, the operator can be within easy reading distance of 

 the scale. 



THE LAMP. 



The temptation to have an electric lamp, preferably 

 affixed to the scale-stand, is great. It offers the advantages 

 of a brighter spot and less halation, but there is always 

 the danger of leakage, and for this reason I recommend 

 a paraffin lamp. A useful type is Fig. 129. There is 

 a lens, across which there is a vertical wire so 

 that the spot of light upon the scale appears 

 as in Fig. 130 ; but it is better, in avoidance of 

 halation, to paint the lens with dead-black, 

 leaving only a vertical line in. wide in the Fig 130> 

 centre. The spot then appears as in Fig. 131, and can be 

 more conveniently and accurately read. 



THE SHORT-CIRCUIT KEY. 



Fig. 132 shows a very useful and reliable 

 form of short-circuit key, but I have found a 

 Fig. 131. cheaper pattern answer quite satisfactorily 

 upon substituting a brass bar for the ebonite one shown 

 in the front of Fig. 133. 



Fig. 132. Fig. 



SHUNTS. 



For research work a shunt in terms of the galvano- 

 meter, and proportions of , $, and 9^, is desirable for 

 use in conjunction with the high-resistance instrument. 



R 



