280 Progress in Science. [April, 



positive pole. When the positive pole rotates, the luminous spots do not 

 rotate with it ; but when the negative pole rotates, and the positive is 

 stationary, the two luminous spots on the positive pole rotate with the nega- 

 tive. If, therefore, a negatively charged cloud should be passing over the 

 earth, and one corner of the cloud be nearer to the earth than the remainder, a 

 luminous ball might possibly be seen running over the surface of the ground, 

 and following the movements of the cloud above. When the cloud came 

 sufficiently near the earth for the spark to pass, there would be a flash of 

 lightning and a crash of thunder. Mr. Varley cautiously observes that this 

 may explain the phenomenon known as ball lightning, which is too well 

 attested to be doubted, but which, from the absence of explanation, has been 

 hitherto unbelieved to be a reality by many men of science. This experiment 

 was shown by Mr. Varley, for the first time in public, at the soiree previously 

 alluded to. 



On the same occasion, another interesting experiment was shown by 

 Mr. Varley, in confirmation of an hypothesis which he mooted at one of the 

 soirees last year, namely, that the stratifications in vacuum tubes are partially 

 or wholly due to the presence of particles of matter detached from the negative 

 pole. Plucker has shown that when a current of electricity is passed from the 

 positive to the negative pole of a Geissler's tube, and the tube is placed over 

 the poles of a very powerful magnet, the light is gathered up, and follows the 

 course of the magnetic rays, no matter what be the direction in which the 

 electric current is flowing. When the electric current and the magnetic rays 

 run parallel to each other, a magnificent arch is produced, which extends on 

 each side of the negative pole, beyond where there is any electric current 

 flowing. Last year Mr. Varley stated, that from the nature of this pheno- 

 menon, he believed the arch to consist of incandescent particles detached 

 from the negative pole, and controlled as to their course by the mag- 

 netic rays. The truth of this conjecture he has since supported by the 

 following simple experiment : — A thin slip of talc, i inch in length, 

 T \jth inch broad, and about -^th grain in weight, is mounted on a single 

 fibre of silk, and suspended inside the Geissler's tube. When this tube 

 is placed over the poles of a powerful electro-magnet in such a position 

 that the luminous arch shall not touch the talc, the passage of the electric 

 current does not put the talc in motion. If the tube be so shifted that the 

 arch plays upon the lower portion of the talc, it repels it. If it be still further 

 shifted, so as to throw the arch against the upper portion of the talc, it is 

 repelled, although in each case, from the position of the poles, there is no 

 electric current whatever passing in that part of the tube which contains this 

 delicate tell-tale. When the arch is allowed to play against the almost invisible 

 fibre of silk which suspends the talc, the fibre is in no way injured. A still 

 further confirmation of the truth of the hypothesis is, that that portion of the 

 arc which strikes the talc produces a luminous cloud brighter than the rest of 

 the arch, indicating that the matter is arrested and condensed there; the 

 remaining portion of the arch is cut off by the intervention of the strip of talc. 



The most singular thing, perhaps, in this experiment is the fact that this 

 transfer or projection of matter from the negative pole, is in the opposite 

 direction to that in which, a priori, it might be expecfed to pass. It is in the 

 reverse direction to that in which particles of carbon are carried between the 

 carbon points of the working electric lamp. Mr. W. R. Grove noticed, many 

 years ago, when experimenting with the voltaic arc in air on a very large 

 scale, that if the negative pole were of platinum, while the positive pole was 

 carbon, there was a transfer of carbon from the positive pole to the negative ; 

 but, in addition to this, particles of platinum appeared on the carbon, they 

 having been transferred from the negative pole to the positive, in obedience to 

 some law at present unexplained. 



METEOROLOGY. 



The Meteorological Office has published Parts II. and III. of its " Quarterly 

 Weather Report for 1869," containing the lithographed curves and explanatory 

 chronicle for the six months from April to October. 



