146 



HARDWICKE'S SCIENCE-GOSSIP. 



its size ; and frequently when chased in a pool, it 

 will charge the invader's hand with a force equal to 

 that of a blow from a stone. When escaping from 

 pursuit over moist gravel, it exhibits a marvellous 

 amount of energy and agility ; and it has been 

 observed, that when thus harassed, the creature 

 invariably, with unerring instinct, shapes a direct 

 course towards the sea, never away from it. When 

 the tide returns, it creeps by its ventral fins into 

 some place of shelter and security ; in fact, this fish 

 exhibits a special predilection for snug and cosy 

 retreats amid the realms of the sea. "With remarkable 

 tenacity of life and a capacious gill-chamber, it leads 

 a sort of amphibious career between the tideless shore 

 and the rock-strewn floor of the adjacent ocean. The 

 shanny spawns during the summer. The ova are 

 deposited in a tiny sea-hall — a species of rock-hewn 

 nest situated near low-water mark ; and the fish 

 guards and watches the progeny with indefatigable 

 vigilance and assiduity. A lavish exuberance of fin- 

 rays clothes the body of this fish. The dorsal fin 

 has usually 31 rays ; the pectorals 13 ; the ventrals 

 2 only, but of eminent service ; the anal has 19, 

 and the caudal about_ II or 13. The colour of 

 the skin varies extremely according to the habitat, 

 &c., of the creature. 



( To he continued^ 



ON CERTAIN PHENOMENA CONNECTED 

 WITH ATMOSPHERIC ELECTRICITY. 



By Walter G. Woollcombe, B.A., F. L.S. 



\Coniinued from fagc 122.] 



I. '7 IGZAG Lightning is a veritable electric spark 

 "^ either between two clouds, or more often 

 between a cloud and the earth. This grand spark is 

 able to divide or bifurcate into two, seldom three, 

 branches, hence the names of " chain " * and 

 "forked" lightning. It proceeds from clouds in 

 which the globules are packed so close as approxi- 

 mately to form compact masses,' and the electricity 

 on their surface is brought most into play. This is 

 but a particular case of De la Rive's theory of clouds. 

 To account for the form we have two theories : 

 one stated by me in Science-Gossip for December, 

 1880, and given by Ganot amongst others, viz., that 

 the lightning seeks to take the path of least resist- 

 ance;! the other is that its form is due to the fact 

 that, in its journey through an electrically-strained 

 medium intervening between the two clouds, the 

 lightning proceeds from one particle of the vapour 

 disseminated in the atmosphere to another, and the 

 zigzag appearance results from the irregularity of the 

 position of these particles. 



* "Nature," xviii. pp. 260, 302. 



t By the way, I niight add thai Herbert Spencer shows that 

 the law of least resistance is followed under every condition to 

 which matter is subject, and even in sociological phenomena. 



2. Sheet Lightning. — De la Rive's theory of clouds 

 gives a very beautiful explanation of this form, viz., 

 that the discharge in this case appears to be made 

 among all the individual components of the cloud 

 with accompaniment of light, thus illuminating 

 either the whole or only the boundary of the cloud, 

 whose different components are like so many spangled 

 panes. Some say, as noted by me, that sheet light- 

 ning is the result of brush discharges from the surface 

 alone, others that it is the reflection of an actual 

 flash which is not visible to us owing to the inter- 

 position of clouds or to its taking place below the 

 visible horizon. 



[The theory of Mr. Parfitt given in the December 

 number, namely, that sheet lightning is an image 

 on our retinas produced by a flash of forked light- 

 ning which has taken place too rapidly to form a 

 distinct impression of its form, seems to me to fail 

 entirely. The outline of the flash would not be 

 distorted, the only result of its taking place too 

 rapidly being to diminish our idea of its brightness. 

 In fact the brightness of every flash of forked light- 

 ning is comparable to that of the sun, and would 

 produce a grand illumination of the surrounding 

 country if it did not vanish too quickly for us to 

 receive a true impression. 



I do not understand what "Scientia" means in 

 his note in the February number, where he states 

 that sheet lightning is an electric discharge taking 

 place between clouds at such a remote distance from 

 each other as to be below the horizon. Surely the 

 fact of being below the horizon is not a condition 

 that clouds should be at a remote distance from 

 each other, or vice z'c?-sd. I presume he means that 

 they are at such a remote distance from us as to be 

 below the horizon. With reference to his explana- 

 tion of the form, .how does he explain the fact that 

 sheet and fork lightning are sometimes seen almost 

 simultaneously in adjacent regions of the atmosphere 

 where the air could not offer at once the two extremes 

 of "great" and " little or no resistance" ?] 



Under this head comes another sort of lightning 

 called "heat lightning," after which thunder is never 

 heard. This form was supposed to be due to a 

 very distant storm, but, as it has been observed 

 overhead in a serene sky, the best explanation is that 

 it is due to discharges between masses of vapour 

 existing in portions of the atmosphere in greater 

 quantities than elsewhere. 



3. Ball Lightning. — The cause of this is totally 

 unknown.* The globes of fire that are seen may 

 be masses of moist vapour powerfully electrified, and 

 becoming luminous by brush discharges all over 



* Professor Tait, in a lecture on " Thunderstorms," refers to 

 those who try to get out of the difficulty by denying the exist- 

 ence of Ball Lightning. One of these is the author of a pamphlet 

 on "Electric Meteorology" lately published in this town, in 

 which pamphlet the main argument is based on the supposition 

 that electricity " by its lig/iiness" can render buoyant particles 

 of water ! and in which certain physical ideas are strangely 

 confused ! 



