152 



Mr. Gustav Bischof on Putrescent [Apr. 19, 



When the heating was not excessive the bubbles did not become motion- 

 less, but their vibrations had a tendency to one side of the cavity, as in 

 fig. 7, D and E. 



The larger bubbles in other cavities were likewise attracted. The 

 vibrating bubbles were generally seen at or near the top of the cavities. 

 Cooled with ether-spray the bubbles ceased vibrating. The microscope- 

 stage was inclined at an angle of 45° throughout the experiments. About 

 fifty different cavities, none of them exceeding the dimensions already 

 given, all behaved in the same way. There were several moving bubbles 

 in cavities a little larger than those already noted; for instance one 

 measured j^ViX x 5 °^ an m ch. The motion never extended across 

 the cavity, but was confined to a sort of shuffling up and down, which 

 shifted the bubble from one side to the other (see fig. 7, D and E). On 

 presenting a warm wire to the cavity the bubble was instantly attracted, 

 and it remained clinging for some time to the side of the cavity. 



Eor an explanation of the cause of vibration I must refer to the fact 

 that I have proved, that gas-bubbles in water as well as in carbonic acid 

 may be attracted by a source of heat giving an extremely slight rise of 

 temperature. It is impossible to imagine a body which is not gaining 

 or losing, or, at the same time, both gaining and losing heat ; it is there- 

 fore impossible to imagine it entirely throughout at a uniform tempera- 

 ture. It is evident, then, that an easily movable particle which can be 

 set in motion by exceedingly slight rises of temperature will make the 

 transference of heat from one point to another plainly visible. I have shown 

 that the minute bubbles in fluid-cavities are such particles ; and I believe 

 that the vibratory motions which I have described afford an ocular de- 

 monstration of the continual passage of heat through solid substances. 



April 19, 1877. 

 Dr. J. D ALTON HOOKER, C.B., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read :~— 



I. " On Putrescent Organic Matter in Potable Water." By 

 Gustav Bischof. Communicated by E. Frankland, F.R.S. 

 Received March 17, 1877. 



It is fortunate that smell and taste are generally extremely sen- 

 sitive indicators of putrefaction in articles of food. This does not, 

 however, apply to drinking-water, which may be largely polluted by 

 putrescent organic impurities without causing any suspicion to our 



