HARDWICKE'S SCIENCE-GOSSIP. 



147 



their surface. They are generally visible from one 

 to ten seconds, and travel from the clouds to the 

 earth so slowly that we may watch their passage 

 with the eye. They sometimes divide, strike the 

 earth, and rebound with a sharp explosion. 



4. Volcanic Lightning.— T^xq clouds of dust, 

 ashes, &c., that are poured forth from volcanoes 

 are accompanied by luminous electric discharges 

 " due to the rapid condensation of the vast volumes 

 of heated vapour" and to friction of the emitted 

 materials. 



Besides the above enumerated forms of light- 

 ning we have brush discharges from tops of edifices, 

 masts of ships, &c., called St. Elmo's fires,* caused 

 by the accumulation of electricity at projections 

 and points under the influence of a passing thunder- 

 cloud. 



One sign of an approaching hurricane, men- 

 tioned in the "Handbook of the Laws of Storms," 

 is said to be lightning of a columnar character 

 shooting up in stalks from the horizon with a dull 

 glare. 



I have attempted to explain the different plausible 

 theories as to the origin and distribution of atmo- 

 spheric electricity, and as to the forms which lightning 

 assumes, so that your readers may choose those which 

 are most in accordance with their own observations. 

 A great deal of the subject is at present involved in 

 mystery, but we must hope that the comparatively 

 new science of meteorology, aided by experiment, 

 will in time solve the difficulties. 



Before I end I should like to allude to a note 

 in Science-Gossip for 1878, p. 237, in which the 

 writer wishes to know whether lightning has ever 

 been seen passing from the earth to the clouds. I 

 may refer him and other inquirers to a lecture 

 delivered by Professor Tait, and chronicled in 

 "Nature," vol. xxii., wherein is the following 

 paragraph : — 



"A remark is made very commonly in thunder- 

 storms which, if correct, is obviously inconsistent 

 with what I have said as to the extremely short 

 duration of a flash. The eye could not possibly 

 follow movements of such extraordinary rapidity. 

 Hence it is clear that when people say they saw a 

 flash go upwards to the clouds from the ground or 

 downwards from the clouds to the ground they must 

 be mistaken. The origin of the mistake seems to 

 be a subjective one, viz., that the central parts of 

 the retina are more sensitive by practice than the 

 rest, and therefore that the portion of the flash which 

 is seen directly affects the brain sooner than the 

 rest. Hence a spectator looking towards either end 

 of a flash naturally fancies that end to be its starting 

 point." 



* The word " Elmo" is supposed to be derived from Helen, 

 who, with her brothers. Castor and Pollux, appeared as"lucida 

 ■sidcra" after storms, according to ancient superstition. — Vide 

 Hor. Carm. iii. 2. 



A STUDY OF THE VARIATION OF THE 

 SMALL TORTOISESHELL BUTTERFLY 

 (VANESSA URTICyE). 



By A. H. SwiNTON. 



Part I. 



THE gradual adherence of naturalists to the 

 modern or Darwinian school in place of the 

 old Linnsean and cruder Fabrician, will doubtless, 

 as was long since surmised, lead to the eventual sub- 

 stitution of synthetical methods for the present pre- 

 vailing analytical ones. The student of nature will 

 be directed to trace out the living and ever-springing 

 branches of the tree of descent, by means of certain 

 ancestral and common features, and certain ancestral 

 and common laws ; and rather than attempting 

 minute scrutiny and exact definitions, which by the 

 law of fluxion can but prove an eventual reductio ad 

 abstirdum, he will now be more fully led to distin- 

 guish by type and most characteristic form. To 

 illustrate the biological reason for this enunciation, 

 I propose to transplant from German soil a few 

 fundamental facts that seem immediately to postulate 

 the gradual evolution and specialisation of butterflies 

 and moths, and which yield fair promise of opening 

 up fresh fields of research. 



Let us take for example the small tortoiseshell 

 ( Vanessa nrticix). What butterfly is more familiar 

 and deserving of study than this earliest harbinger of 

 our English spring and latest spirit wanderer over the 

 fallen russet of autumn ? Who recalls not with delight 

 the sharp autumn hour when he first heard its wings 

 beating up the window pane ; or who retains not the 

 memory of that strange sentiment that arose, when 

 the dark-winged intruder was afterwards dislodged 

 from some snug parlour corner or cobwebbed out- 

 house when the snow lay at Christmas? Of all 

 bright life, this being that flies so puzzlingly about 

 the heliotropes and gravelled walks, communes most 

 with our better aspirations and incites most the 

 curiosity. Even as I write, while the cold wind 

 soughs drearily in the chimney and the boughs lie 

 bare in the late spring, there exists a secret pleasure 

 in the thought that, three weeks ago, a bevy of tor- 

 toiseshells and brimstones were to be seen fluttering 

 out at warm noonday on the metropolitan coach 

 road. They are all back now to their sleep of 

 beauty beneath the ivied wall and clematis-twined 

 porch, and I, their meditative historian, draw my 

 chair closer to the hearth to escape the chill and 

 rheums of a windy equinox. 



But what is better than a picture to recall the 

 absent, and how can a picture be sweeter than when 

 it portrays nature encompassed with the grace and 

 illusions of the morning ? Of all observers the late 

 Edward Newman could perhaps best appreciate the 

 line of beauty in Urticse, and on re-opening his great 

 work on butterflies I find the desired likeness in a 



H 2 



