477 



into pla}' here. Zeehlizen '), howevei', has detected that also saponins 

 and aniipyretira, which do not smell, produce an electrical charge. 

 This, therefore, is not a property pecnliar to odorous substances 

 alone. 



Tyndall*) previously observed that several odorous substances 

 possess a great capacity of absorbing- obscure rays. We might, 

 therefore, expect a correlation between these two properties, as it is 

 quite possible that odorous substances derive energy from their 

 surroundings to transmit it to the olfactory organ. 



If so, we must expect smell-intensity and absorbing capacity in 

 different odorous substances to evince, if not proportionality, at all 

 events parallelism. 



On Prof. Zwaardemaker's suggestion I undertook an investigation 

 in this direction. 



Since I purposed merely a preliminary orientation with regard to 

 this problem, there was no need of being very accurate, so that 

 many difficulties could be avoided. 



1 determined the absorptive capacity of dry air that had passed 

 through a slightly curved tube filled with the fluid under examination 

 and compared it with the capacity of pure dry air by a differential 

 method. 



On either side of a Nernstlamp a glass tube was placed closed 

 at both ends with a plate of rocksalt. Behind these tubes were 

 arranged Moll's t her mo-piles connected oppositely with a Moll 

 galvanometer. Air or gas could be sucked through one of the tubes 

 by means of a spirometer. In front of the other tube an irisdiaphragm 

 was mounted, the area of which could be read from a large pro- 

 tractor. The width of the opening, corresponding to every scale- 

 division, was determined by measurement. 



The deviation of the galvanometer was measured by the movement 

 of the reflected image of an illumined copperwiie on a millimeter- 

 scale. For every determination dry air was first passed through the 

 one tube, and then the diaphragm adjusted so as to make the 

 galvanometer point to zero. This could readily be done, as the 

 apertures in double screens, interposed between the lamp and the 

 measuring tubes, could be coxered or uncovered at the same moment. 



Subsequently air was sucked for al)Out ten minutes through the 

 fluid under examination, and through the measuring tube. After 

 this the diaphraghm was so adjusted that again removal of the 



1) These Proc XX p. 1-272. 



') J. Tyndall: Heat as a mode of motion p. 366. 



