Decembek 29, 1911] 



SCIENCE 



917 



DISCUSSION AND COBSESPONDENCE 



THE POSITIVE lOiSr IN ELECTRICAL DISCHARGE 

 THROUGH GASES 



When a metal sphere is hung upon a silk 

 cord between the terminals of a plate glass 

 electric machine, it will oscillate to and fro 

 between the terminals. 



When molecules of a gas are placed in a 

 similar position, they can not behave in quite 

 the same fashion. No one molecule can plow 

 its way through the swarm of molecules which 

 surround it. They are all being urged to do 

 this. At any instant some are being urged 

 away from the positive terminal, and some 

 from the negative. These opposing streams of 

 gas mingle. The collisions which result be- 

 tween these overcharged and undercharged 

 molecules within such a field of force result 

 in a continual transfer of electrical corpuscles 

 from molecule to molecule. In such a mixture 

 we should at auy instant expect to find three 

 classes of molecules. Those which are nega- 

 tively overcharged, those which are negatively 

 undercharged, and those which are in normal 

 condition. 



Even in open air discharge, the repelled 

 molecules move along streamers. In partic- 

 ular is this the case at and near the positive 

 terminal. Here the corpuscles and air mole- 

 cules are moving in opposite directions. In 

 rarefied gas, where the mean free path is 

 greatly increased, these streamers become 

 « rays." 



All of the properties of these rays are in 

 harmony with what we should expect, from 

 our knowledge of the behavior of the metal 

 ball and the properties of gases. 



Francis E. Niphee 

 Washington Univeesitt 



a new record of a chestnut-tree disease 

 in mississippi 



Professor Eugene Hilgard, of Berkeley, 

 Cal., told me this summer of an observation of 

 his which is of moment to those interested in 

 the chestnut-bark disease. 



While surveying in 1856 in the northeastern 

 part of Mississippi, he found the chestnut 

 trees of that region, both young and old, dead. 



They had been growing in a mixed forest of 

 pine and oak and, as the other trees were in 

 a healthy condition, were very noticeable. The 

 dead trees were frequently of large propor- 

 tions, attaining a height of 80 to 90 feet. 

 When he saw them, these trees were beginning 

 to decay; the bark was dropping off, leaving 

 the trunks bare. There were no signs of in- 

 sects. The region which was surveyed is a 

 non-calcareous one. 



As chestnuts are still growing in northeast- 

 ern Mississippi, the epidemic which Professor 

 Hilgard saw did not exterminate the tree in 

 that region. It is another record of a devasta- 

 ting disease which the chestnut tree has en- 

 dured. 



Now that extra attention has been given to 

 the chestnut and old records have been looked 

 over, the struggle which this tree has had 

 against attacks of fungi and of insects during 

 the nineteenth century becomes apparent. 

 There can hardly be a doubt but that the 

 present range of this tree is much less ex- 

 tensive than formerly. 



Caroline Eumbold 



BLANDING's TURTLE 



To THE Editor of Science: Eef erring to 

 Mr. Howe's note in Science of September 1, 

 " Second Record for Blanding's Turtle in 

 Concord, Mass.," and of the introduction of 

 three pairs of the same species in Little Long 

 Pond, Orange County, by Dr. Townsend, I 

 beg leave to report finding this turtle at 

 Queens, L. I., in June, 1909. It has been 

 placed on the records of the Natural History 

 Survey of Long Island now being made by 

 the Brooklyn Institute of Arts and Sciences. 

 This is the first report, so far as we know, of 

 Blanding's turtle having been found on Long 

 Island, but Abbott in " A Naturalist's Eam- 

 bles about Home" mentions finding it in 

 central New Jersey. 



John J. Schoonhoven 



the moth of the cotton worm 

 To the Editor of Science: In connection 

 with the notices appearing in Science (Oc- 

 tober 16 and November 10) recording the oc- 

 currence far north of the moth of the cotton 



