ELECTRICITY. 



283 



the tip of the flame, the instrument showed a posi- 

 tive deflection of T0to 80. 



Experiment 4. With the testing-plate five milli- 

 metres from the outer surface of the flame, on all 

 sides, a feeble positive charge was obtained, the air 

 in contact with the flame being apparently charged 

 positively, the indication in no case exceeding 50 or 

 60 on the scale of the electrometer. 



Experiment 5. The metallic tip of the burner was 

 found to be charged positively, giving an indication 

 closely agreeing in the number of degrees with that 

 corresponding to the negative indication of the 

 flame. The indication was quite constant. 



Experiment 6. When a glass tip was substituted 

 for the metallic tip, no charge was found upon it. 

 This was the case when any non-conducting body 

 formed the tip. 



Experiment 7. A glass tip haying been substi- 

 tuted for the metallic one, a platinum wire was in- 

 serted below the orifice and carefully pushed upward 

 until it occupied the centre of the interior cone of 

 flame. A very feeble indication of negative electri- 

 city was the result. While, with the Bunsen burner, 

 the flame and the metallic tip are in decided elec- 

 trical opposition, the one having a negative and the 

 other a nearly equal positive charge, in spirit-flames 

 the two opposite states recombine, the wick of the 

 lamp and the fluid contained in the. vessel connect- 

 ing the two charges. The flame, therefore, merely 

 takes the potential of the atmospheric electricity at 

 the place where it is situated. 



The conclusions to which these experiments 

 lead are thus given : 



1. The flame of a Bunsen burner is negative, while 

 positive electricity accumulates on the burner itself, 

 if it is a good conductor. With orifices made of noni 

 conductors, no charge was found upon the tip. 



2. The stratum of air in contact with the outer 

 cone of flame is slightly charged with positive elec- 

 tricity. The partly-consumed gas or the interior 

 cone is neutral. 



3. The pressure of flames tends to change the na- 

 ture of the atmospheric electricity at the given place, 

 reducing a positive tension to a feebly negative one. 

 American Journal of Science. 



Passage of Electricity through Gases. MM. 

 "WiedemannandKuhlmann have experimented 

 on the passage of the electric current through 

 various gases. The electricity was obtained 

 from a Holtz machine, and tlie discharge pro- 

 duced within a cylindrical metallic vessel, in 

 which the electrodes, insulated from the ves- 

 sel, and terminating in metallic knobs, were 

 confined. By a system of tubes, the air could 

 be rarefied, and different gases introduced. The 

 intensity of the currents was measured by a 

 reflecting galvanometer, and the interval be- 

 tween the discharges determined by a heliom- 

 eter and rotating mirror. The following are 

 some of the results obtained : 



Varying the velocity of the machine (other circum- 

 stances being the same), it was first of all observed 

 that the quantity of electricity produced by a con- 

 stant angular displacement, <fr, of the plate of the 

 machine is independent of the speed of rotation. 

 When other circumstances varied, as, e.g., the de- 

 gree of humidity in the air, or the distance between 

 e two plates of the machine, the intensity of the 

 jurrent, as shown by the galvanometer, varied also 

 (the speed of rotation being constant), and the inter- 

 Is separating the discharges were found inversely 

 proportional to the quantity of electricity, as meas- 

 ured by the galvanometer. Thus, the quantities of 

 electricity which pass between the electrodes at each 

 discharge are always the same, all the circumstances 

 being equal. 



The changes in appearance of the discharge, ac- 

 cording to the nature and pressure of gas, are well 

 known. 



The intervals between successive discharges di- 

 minish as the pressure diminishes. At the lowest 

 pressure employed. % or % mm., discontinuous dis- 

 charges were still obtained, which were distinguished 

 by the rotating mirror. Thus, a continuous electric 

 discharge is not produced in rarefied gas, and re- 

 quires for its production a determinate tension in 

 such media. 



As to pressure, the experiments (of which there 

 were eight different Aeries) were made with air, dry, 

 and freed of carbonic acid. The experiments show 

 that, for equal quantities of electricity in the elec- 

 trodes, the interval between the successive dis- 

 charges, and hence the quantity of electricity neces- 

 sary to produce a discharge, increases in proportion 

 to the pressure. This increase is most rapid at low 

 pressures. 



As to the nature of the gases : six gases were ex- 

 perimented with, the electrode balls being of plati- 

 num, about 3.40mm. diameter each, distant 9.2mm., 

 and sometimes connected, sometimes disconnected, 

 with the ground. It was found that, for a constant 

 intensity of current, the interval between the dis- 

 charges is nearly the same, in equal pressure, for air, 

 oxygen, nitrogen, and carbonic acid; it is much 

 smaller in hydrogen, and much greater in sulphurous 

 acid. 



As to the nature of the electrodes : the same ex- 

 periments were repeated with the six gases, varying 

 the electrodes. It was found that, so long as the dis- 

 charges are slowly transmitted by a rarefied gas, the 

 substance composing the electrodes does not influ- 

 ence the interval of the discharges. 



Two balls of brass were used, one 13.8 mm. in di- 

 ameter, the other 2.65mm., and their distance apart 

 was varied, the intensity of the current remaining 

 constant. The results obtained are represented by 

 two curves, having for abscissae the distances of the 

 electrodes, and for ordinates the intervals of the dis- 

 charges. The form of these curves is seen to be 

 completely different, according as the large ball is 

 negative or positive. It was found that, when the 

 distance between the electrodes has reached a certain 

 extent, then, to produce a spark at such distance, a 

 much greater quantity of electricity is necessary 

 when the large ball is negative than when it is posi- 

 tive. Moreover, when the large ball is positive, the 

 quantity of electricity necessary to a discharge quick- 

 ly reaches a maximum, while it increases rapidly in 

 the inverse case, in proportion as the distance be- 

 tween the electrodes increases. 



Measuring Atmospheric Electricity. Prof. 

 Palmieri, in his observatory on Mount Vesuvi- 

 us, has a delicate contrivance for this work. 

 A disk of metal is placed above the roof of the 

 observatory, and connected by an insulated 

 metallic rod with a gold-leaf electroscope and 

 a bifilar electrometer (in a room below), which 

 are observed regularly. He deduces from his 

 researches the following law : If, within a dis- 

 tance of about fifty miles, there is no shower 

 of rain, hail, or snow, the electricity is always 

 positive; the single exception is during the 

 projection of ashes from the crater of Vesuvi- 

 us. During a shower he finds the following 

 law universally to hold good : At the place of 

 the shower there is a strong development of 

 positive electricity; round this there is a zone 

 of negative, and beyond this again positive. 

 The nature of the electricity observed depends 

 upon the position of the observer with respect 

 to the shower, and the phenomena will change 

 according to the direction in which the shower 



