228 



NATURE 



[Jan. 17, 1878 



suggests that if we had powerful enough telescopes, the 

 neighbourhood of the nebulas should be searched to dis- 

 cover stars capable of exercising such a magnetic in- 

 fluence. If such a star was found likely to act thus on 

 any nebula, then the line passing through the centre of 

 the nebula and the star should be searched to discover if, 

 at the other magnetic pole of the star, a second nebula 

 did not exist, with its spirals in a contrary direction to those 

 of the former. 



M. Plant<f states that with a much more intense source of 

 electricity he has observed small luminous rings, composed 

 of incande; cen t particles, altogether detached from the elec- 



Fig. 5. — Luminous globule formed at the surface of a liquid by an electric 

 cuirent of high tension. 



trode. These rings, the centre of which was agitated by 

 a small liquid whirlpool, moved in the interval comprised 

 between the electrode and a very large luminous ring 

 formed round about by the shock of the electric current 

 against the sides of the voltameter. 



The Formation of Hail. — In a paper in the Comptes 

 Rendus, t. Ixxxi. p. 616, M. Plants had shown the influence 

 which atmospheric electricity in a state of discharge must 

 have in the formation of hail, not by producing the cold 

 necessary to congelation, as is sometimes supposed, but 

 by exercising, on the contrary, a powerful heating action, 



Fig. 6. — Shower of aqueous globules produced by a current of double the 

 tension of the preceding. 



capable of rapidly vaporising the moisture, and of project- 

 ing the vapour into the cold regions of the atmosphere. 

 To succeed in explaining the part played by electricity in 

 this natural phenomenon, it is necessary to point out the 

 mechanical action which may result from the passage of 

 the electric fluid into the midst of aqueous masses, and 

 thus to project into the air liquid globules susceptible of 

 being transformed into hailstones. 



In previous experiments iM. Plants showed that with an 

 intense source of voltaic electricity, the immersion of the 

 positive wire in a conducting liquid, such as salt water, 

 determines the aggregation cf aqueous molecules around 



the electrode in the form of a luminous spheroid, in con- 

 sequence of a double simultaneous effect of flow and 

 aspiration, or of passage in two directions which seems 

 peculiar to the electric current (Fig. 5). 



But by employing a current still more intense, resulting 

 from the discharge of a battery of 400 secondary couples, 

 he obtains, by the immersion of the positive wire, instead 

 of a single globule, a shower of innumerable ovoid 

 globules, which succeed each other with excessive 

 rapidity, and are projected to more than a metre distance 

 from the vessel in which the experiment is made. The 

 spark produced at the same time at the surface of the 

 liquid presents the form of a corona or aureole of many 

 points, from which burst forth the aqueous globules 

 (Fig. 6). 



The metallic property of the electrode is not neces- 

 sary to obtain this effect. A fragment of filter paper, 

 moistened with salt water, in communication with the 

 positive pole, also produces the phenomenon, and con- 

 stitutes a humid mass analogous, to a certain point, with 

 that of a cloud from which proceeds an electric current. 

 If, instead of encountering a deep layer of liquid, the 

 current meets with a moist surface such as the sides or 

 the inchned bottom of a basin, the heating effects pre- 

 dominate, the aureole is very brilliant, and the water is 

 rapidly transformed into vapour (Fig. 7). 



The action of the current then differs according to the 

 resistance which is opposed to it, and we find here a new 



Fic, "7, — Jets of vapour and luminous streaks produced by an electric 

 current of high tension on meeting with a moist surface. 



example of the reciprocal substitution of heat and mecha- 

 nical work resulting from the electric shock. When the 

 work represented by the violent projection of the liquid 

 appears, there is neither heat nor vapour developed, and 

 when no visible work is accomplished, when the liquid is 

 not projected, heat is engendered and vapour disengaged. 

 M. Plantd sums up the results of these experiments 

 thus : — 



1. Electric discharges produced in the midst of clouds 

 may, according to the greater or less density of these 

 moist conductors, determine their reduction into vapour, 

 or their instantaneous aggregation into globules of a 

 volume much greater than that of the globules of the 

 cloud, and the liquid bombs thus formed may be pro- 

 jected to great heights, where the temperature is notably 

 lower than that of the medium in which the discharges 

 are produced. 



2. The formation of hailstones, in the case where they 

 do not present a series of opaque and transparent layers, 

 but a structure radiating from the centre, is also explained 

 by such a mechanical action ; they must be produced by a 

 single jet, and congealed under the same volume which 

 they had at the moment when they were shot forth by the 

 electric current. 



3. The ovoid or pyramidal form of these hailstones, as 

 also their angular parts, aspirates or protuberances, are 

 due to their electric origin. 



