•OciOBEE 4, 1895.] 



SCIENCE. 



437 



electric filters we have made many other 

 experiments to find other means for the dis- 

 electrification of air. It might be supposed 

 that drawing air in bubbles through water 

 should be very effective for this purpose, 

 but we find that this is far from being the 

 case. We had previously found that non- 

 electrified air drawn in bubbles through 

 pure water becomes negatively electrified, 

 and through salt water positively. We 

 now find that positively electrified air drawn 

 through pure water, and negatively electri- 

 fied air through salt water, has its electrifi- 

 cation diminished but not annulled, if the 

 primitive electrification is sufficiently 

 strong. ISTegatively electrified air drawn 

 in bubbles through pure water, or posi- 

 tively electrified air drawn through salt 

 water, has its electrification augmented. 



§ 11. To test the effects of heat we drew 

 air through combustion tubes of German 

 glass about 180 cms. long, and 2^ or Ih cms. 

 bore, the heat being applied externally to 

 about 120 cms. of the length. We found 

 that, when the temperature was raised to 

 nearly a dull red heat, air, whether posi- 

 tively or negatively electrified, lost little or 

 nothing of its electrification by being drawn 

 through the tube. When the temperature 

 was raised to a dull red heat, and to a 

 bright red, high enough to soften the glass, 

 losses up to as much as four-fifths of the 

 whole electrification were sometimes ob- 

 served, but never complete diselectrifica- 

 tion. The results, however, were very 

 irregular. Non- electrified air never be- 

 came sensibly electrified by being drawn 

 through the hot glass tubes in our experi- 

 ments, but it gained strong positive electri- 

 fication when pieces of copper foil, and 

 negative electrification when pieces of car- 

 bon, were placed in the tube, and when the 

 temperature was sufficient to powerfully 

 oxidize the copper or to burn awaj' the 

 .charcoal. 



§ 12. Through the kindness of Mr. E. 



Matthey, we have been able to experiment 

 with a platinum tube 1 metre long and 1 

 milUmetre bore. It was heated either by a 

 gas flame or an electric current. When 

 the tube was cold, and non-electrified air 

 drawn through it, we found no signs of 

 electrification by our receiver and electrom- 

 eter. But when the tube was made red 

 or white hot, either by gas burners applied 

 externally or by an electric current through 

 the metal of the tube, the previously non- 

 electrified air drawn through it was found 

 to be electrified strongly positive. To get 

 complete command of the temf)erature we 

 passed a measured electric current through 

 20 centimetres of the platinum tube. On 

 increasing the current till the tube began to 

 be at a scarcely visible dull red heat we 

 found but little electrification of the air. 

 When the tube was a little warmer, so as 

 to be quite visibly red hot, large electrifica- 

 tion became manifest. Thus 60 strokes of 

 the air pump gave 45 scale divisions on 

 the electrometer when the tube was dull 

 red, and 395 scale divisions (7 volts) when 

 it was a bright red (produced by a current 

 of 36 amperes). With stronger currents, 

 raising the tube to white-hot temperatui'e, 

 the electrification seemed to be considerbly 

 less. 



SCIENCE OR POETRY. 



The hardest of intellectual virtues is 

 philosophic doubt, and the mental vice to 

 which we are most prone is our tendency 

 to assume that lack of evidence for an 

 opinion is a reason for believing something 

 else. 



This tendency has value in practical mat- 

 ters which call for action, but the man of 

 science need neither starve nor choose, and 

 suspended judgment is the greatest triumph 

 of intellectual discipline, although vacilla- 

 tion brands the man of affairs with weak- 

 ness. 



Anything which is conceivable may be 



