17S 



• KNOVv'LEDGE <• 



[Aug. 11, 1882. 



tLe disgrace of gods and men." " Loki is first god, then 

 god and de^-il combined, and finally devil /iiirct simple." 



In her article on " Mischief in the Middle Ages " Miss 

 Robins carefully delineates the liumorous side of the 

 English people. Tlie middle English had a great fund of 

 quaint humour, and a fine capacity for enjoyment. They 

 had also a lively appreciation of the ludicrous and gro- 

 tosque, and were fond of punning devices and mottoes. 

 The mischievous nature of the Norseman, too, w as in the 

 people, but we have not space to go into the evidence which 

 Miss Robins has collected. " As distinct as the mythology 

 of Greece or Scandinavia," s.iys she, " was the fairy mytlio- 

 logy of medi.Tval Europe. It borrowed from the one grace 

 and sensuous recklessness, from the other ruggedness and 

 humour, and formetl a whole of sprightly mischief." The 

 fresh humour of fairy-land is indeed the charm of medieval 

 literature. 



It is curious to note in these articles how the spirit of 

 the nations has been influenced Ijy the circumstances and 

 climates in which they have lived, for the humour of the 

 Hindus was inspired by fatalism, that of Greece by 

 philosophy, of .Scandinavia by hardship and warfare, and 

 that of England by the romantic and progressive spirit of 

 the Ant'lo-Saxon race. JouN Leyl.vsd. 



FORMS OF CLOUDS. 



By the Editor. 



'INHERE are few more interesting and instructive 

 X subjects of study, especially at this season of the 

 year, when so many persons have daily before them a wide 

 stretch of sea horizon, than the clouds — whether they be 

 tlif light feathery clouds called cirrus, which lie often 

 more than ten miles above the earth's surface ; or the 

 cumulus clouds, like great masses of cotton-wool, which 

 form on a summer's day at heights probably varying 

 Ix-tween lialf-a-niile, or less, and two, or, at the outside, 

 three miles from the surface ; or stratus clouds, forming a 

 vast sheet e.xtending to the horizon, or near it; or the 

 various forms of cloud which accompany storms, whether 

 of wind or rain or thunder. 



In the first place, it is interesting to compare our 

 first ideas as to the forms of cloud-masses with those 

 which arise so soon as we reason a little on the subject. 

 It is to be noticed that the cloud-strewn sky is always 

 full of illusions, whatever the shapes of the clouds may 

 t>c, and that, in certain cases, we are under the influence 

 of an absolute illusion quite beyond the power of any 

 reasoning to correct. 



c/>cfO'^'^'°^^C> 



When we look at a distant landscape, and see behind 

 ailUand trees and buildings, the clouds in a sky — or an 

 ii.solutely cloud-covered sky — api)arently extending up- 

 A ards from the horizon it8<;lf, we are unable to resist tlie 

 liiuiiion that the surface which thug forms a background to 

 objfcta at which we look horizontally, is itself either 

 vertical or nearly so. Thus, to take the case of a sky over 



which clouds are freely scattered. If we think of the 

 clouds overhead at all, the idea we form of the sky canopy 

 is that its shape in section is somewhat like what is shown 

 in Fig. 1, where the rounded clouds fully outlined are sup- 

 posed to be cumulus and the others to bo cirrus. If we 

 limit our attention to parts of the sky near the horizon, wc 

 arc very apt to imagine that the cloud-surface seen at A or 

 15 — which often appears continuous even when the clouds 

 overhead are widely scattered — is upright. 



Now, in reality, on a day when the air in which cumu- 

 lus clouds are suspended (to use an inexact but convenient 

 tt'rm) is very clear, as it often is, the cloud-surface which 

 is the background to hills, trees, and liuildings forming 

 the landscape in any direction, is much more nearly hori- 

 zontal than vertical The shape of the cloud canopy, 



o OxDOooo obooo o oo O a 



Fig- 



instead of being what is represented in Fig. 1, is more like 

 what is represented in part only (for very obvious reasons) 

 in Fig. 2, where, however, the layer of cirrus clouds is 

 scarcely shown high enough. 



The real shape of the under surface of a layer of clouds 

 two miles above the surface of the earth is, of course, what 

 is shown in section in Fig. 3, where D is supposed to be 

 the point over head, — if only AB be drawn long enough 

 or OD short enough. But it would be impossible to show 



this projierly on any scale available in the pages of 

 KxowLKDUE. If EOc represents the surface of the earth, 

 ADB the surface two miles above that of the earth, and 

 AOB the horizon plane of the spectator at O, the distance 

 AO can be determined as follows : — Draw the diameter 

 DCc^, which is roughly about 8,000 miles; then we know 

 that 



the square of AO is equal to the rect DO, Ocf. 

 = 2x8,000 

 if we take the mile for our unit of length. Thus 



A0= v/rG;000=127 miles. 

 If we had taken the true diamettir of the earth, we should 

 have made AO equal to 126 miles, — the difference being 

 not worth noticing. Thus we ought, in Fig. 3, to have AO 

 more than si.xty times as long as DO ; so that if DO were 

 a quarter of an inch long — and a shorter distance would be 

 inconveniently small— AO would be nearly IG inches, and 

 AU would want only about five inches of a yard. On the 

 scale of Figs. 1 and 2, in which the height OD is one inch, 

 the points corresponding to A and B of Fig. 1 should be 

 each more than five foot from O. 



Thus the surface of the cloud-layer which forms the back- 

 ground of a distant landscape is very nearly horizontal in 

 this ca.se. It is still more nearly horizontal if the clouds 

 are lower. Suppose, for instance, the clouds half-a-mile 

 high. Then, putting OD in Fig 4 equal to half-a-milo, we 

 get AO=v/4000 = C3 miles, or AO is 120 times as great 

 as DO. 



