Sept. 26, 1884.] 



♦ KNOV^^LEDGE ♦ 



253 



Having, however, thus shown that, given the velocity 

 and elevation of a particle and the latitude of the point of 

 projection, the actual path (apart from atmospheric resist- 

 ance) may be dealt with precisely like the path of a body 

 in space around a centre of attraction, I forbear to deal 

 thus with any given example, simply because there would 

 be no particular use in working out a problem of the sort. 

 The student who cares to do so may thus deal with such a 

 problem, noting that D and m are given in all tables of 

 lunar elements, r is known, ?* for a given latitude is also 

 known, while v and t are supposed to be given. 



(To he contiimed,') 



EDUCATION. 



AT no period of our national history has education 

 assumed the vital importance which now attaches to 

 it. Compulsory as it now is in every rank of life, the man 

 who would even hold his own in the present day cannot, 

 and must not, be contented with the acquisition of the 

 minimum of knowledge ; for assuredly the " survival of the 

 fittest" in the immediate future means that of the possessor 

 of the most varied and best-digested information. We 

 write at the beginning of the educational year, when many 

 hundreds or thousands of young men are commencing a 

 career at the Universities, hospitals, &c., ic, which is 

 either to make or mar them ; to produce citizens who 

 shall contribute to the honour, dignity, and intellectual 

 and material advancement of their native land ; or to turn 

 out failures, who can only act as a clog and a dead-weight 

 upon it. That the study of the classics, with that refining 

 influence which they have exercised upon so many genera- 

 tions of English gentlemen, and of mathematics, with the 

 incomparable mental gymnastics which they supply, will 

 ever be superseded as essentials, it would be idle to suppose. 

 What, though, we would insist upon here is the paramount 

 necessity of supplementing them by a competent acquaintance 

 with natural and physical science. No man, towards the 

 end of this nineteenth century, can be said to be 

 "throughly furnished" who is unfamiliar with the most 

 recent results in physics and biology ; for the value of a 

 knowledge of science can hardly be over-estimated. In its 

 very lowest aspect, the power it confers of increasing our 

 material prosperity might well commend it to those whose 

 first question would be, " Does it pay ? " But for its applica- 

 tion to mechanical and industrial pursuits we could assuredly 

 never have attained that proud pre-eminence among nations 

 which is the glory of every patriotic Englishman. In a 

 higher point of view, though, the earnest student will appre- 

 ciate the benefits it confers, not only as a means of mental 

 training, but for the habit of mind which it induces of loving 

 truth tor its own sake, and humbly pursuing it in the con- 

 fidence that whithersoever it may lead us, it will be into 

 safe and pleasant pastures. And, in the highest point of 

 view, is not the theologian more indebted to science than 

 he is unfortunately always willing to confess 1 No one 

 can fail to contrast the ancient view of the Deity as 

 (what Matthew Arnold calls) " a magnified, non-natural 

 man," a mere tribal ruler, with the immeasurably 

 enlarged conception of the Almighty Lord of the uni- 

 verse enjoyed by the modern student of astronomy, who 

 stands humbled and appalled before majesty so infinite, 

 that he trembles at the very conception of it. If, then, 

 we have not claimed too much for science as an essential 

 element in education — as assuredly we have not — we need 

 not reiterate our earnest advice to the student by no means 

 to neglect it. Even as ci nieaus of recreation, he will find 



it delightful. We are the more encouraged to urge this 

 from the success which our own endeavours to present 

 sound and accurate scientific information — " plainly worded 

 and exactly described ' — have met with. From Canada, 

 from New Zealand, from Burmah, from South America, and 

 from the Cape do we receive testimony that our eflbrts to 

 popularise the knowledge of nature is appreciated. We 

 would fain hope that our fellow countrymen at home may 

 learn widely to value such knowledge, too; and by sedulous 

 study of the marvels by which they are surrounded, supply 

 themselves with one of the most potent weapons available 

 in the battle of life. 



THE ENTOMOLOGY OF A POND. 



By E. A. Butler. 

 THE BOTTOM (continued.). 



SCATTERED about here and there over the bottom of" 

 a clear pond may often be seen a number of dark 

 and more or less cylindrical objects lying horizontally. A 

 little watching will reveal the fact that they are living, for 

 they will be seen slowly movins; about over the bottom, 

 and, perhaps, presently climbing the stem of some aquatic 

 plant. Fishing some out with a net, we find that each 

 consists of a cylindrical tube made of various materials, 

 and inhabited by a sort of caterpillar furnished with six 

 legs on the anterior part of its body. They are caddis 

 worms, or case-worms, but, notwithstanding the name, they 

 have only a very remote connection with the true worms, 

 being the larval forms of the order Trichuptera, i.e., the 

 caddis-flies or water-moths. 



It is not an easy matter to extract the living occupant 

 from its abode by mere pulling, though it is not in any way 

 attached thereto. In such an animal as a snail, whelk, or 

 winkle the ditficulty of extracting the mollusc arises from 

 the fact that it is fastened by strong muscular adhesion to 

 the shell it constructs, but the caddis larva, like the marine 

 tube-worms, merely builds up a case round itself for pro- 

 tection, and is not in any way organically united with it. 

 But by means of certain hooks at the end of its body, it 

 can, like a hermit crab with the molluscan shell it has 

 appropriated, resist very successfully any attempts to drag 

 it lorth, and will even suflTer itself to be pulled in twain 

 rather than relax its hold. An application of boiling-water, 

 however, at once kills the little tenant, and we can then 

 easily draw out its corpse and examine the case at leisure. 

 Should it be desired to extract the animal alive, it must be 

 attacked from the rear. The case is open at both ends, 

 the hinder aperture being the smaller of the two. The 

 head of a pin inserted at this opening and pushed gently 

 forward will so startle the grub as to cause it to relax its 

 hold and advance a little in the tube ; a few more gentle 

 " prods " from behind and it completely evacuates its 

 fortress, without damage to itself or injury to its case, into 

 which it will be ready to return at the first opportunity. 

 On slitting open the case we find that the inside is beauti- 

 fully lined with a tough, thin, papery substance, which is 

 smooth enough, whatever may be the irregularities outside. 

 This material, like the silk of the silkworm, is produced 

 by the insect as a gummy secretion which hardens imme- 

 diately on exposure. 



The nature of the external adornment will depend, upon 

 the species we have secured, and upon the materials that 

 may happen to have been obtainable by the larva. Small 

 bits of stick, rushes, roots, or fibres, blackened by long 

 soaking in the water, and completely water-logged, grains 



