When this globule has reached a sufficient size, you can see it detach itself from the point, which ceases to be luminous, begin to move forward slowly on the plate, make a few curves, and then set off for the positive point; when it reaches this, the effluvium is extinguished, all luminous phenomenon ceases, and the machine acts as if its two poles were united by a conductor. The speed with which the luminous globe moves is very slight. It takes from one to four minutes to cover a distance of 5 to 6 centimetres. Sometimes, before reaching the positive point, the globe bursts into two or more luminous globules, which individually continue their journey towards the positive point. On developing the plate, you will find traced on it the route followed by the globule, the point of explosion, the routes resulting from the division, the effluvium round the positive point. Also, if you stop the experiment before the arrival of the globule at the positive point, the photograph will only give the route to that point. The globule makes its course the conductor. If during its journey you were to throw powder on the plate--sulphur, for example--the course it followed will be marked by a line of little aigrettes, looking like a luminous rosary. Of all the known electric phenomena, this is the most analogous with globular lightning. [Illustration: PHOTOGRAPH OF THE POSITIVE POLE OF AN ELECTRIC SPARK.] [Illustration: PHOTOGRAPH OF THE NEGATIVE POLE OF AN ELECTRIC SPARK.] But the really complicated part of the question is when ball lightning loses part of its fluidity and becomes a semi-solid body, as in the following instance:-- On April 24, 1887, a storm burst over Mortrée (Orne), and the lightning literally chopped the telegraph wire on the route to Argentan for a distance of 150 yards. The pieces were so calcinated that they might have been under the fire of a forge; some of the longer ones were bent and their sections welded together. The lightning entered by the door of a stable in the form of a fireball, and came near a person who was preparing to milk a cow; then it _passed between the legs of the animal_, and disappeared without causing any damage. The terrified cow raised itself on its hind legs with frantic bellowing, and its master ran away, frightened out of his wits, but there was no harm done. The inexplicable phenomenon was that at the precise moment when the lightning crossed the stable, a great quantity of incandescent stones fell before a neighbouring house. "Some of these fragments, of the size of nuts," wrote the Minister of Post and Telegraphs at the Academy, "are of a not very thick material, of a greyish-white, and easily broken by the fingers, giving forth a characteristic odour of sulphur. The others, which are smaller, are exactly like coke.