460 



♦ KNOWLEDGE ♦ 



[Dec. 5, 1884. 



make havoc with the tissues of any insect that once gets 

 within range of their action. The head is attached to the 

 thorax by a very slender junction, and can, therefore, to 

 some extent, be rotated thereon. When the insect is dead, 

 this slendemess of attachment is a serious trouble to the 

 collector, as his dried specimens manifest great readiness 

 to part with their heads if at all rudely handled, or even 

 if suddenly jarred, and he is then fain to collect the scattered 

 members and gum them on again to the best of his ability. 

 With equal, or even greater, readiness do the long slender 

 bodies break off, and to guard against such a calamity, 

 collectors have been recommended to run a fine piece of 

 wire up the body while it is still fresh, and fix one end of it 

 firmly in the thorax. 



The male carries at the end of his abdomen some ap- 

 pendages which are, no doubt, partly responsible for the 

 rustic theory of stinging, before alluded to ; but they are 

 simply clasping organs used by the gentleman for the 

 abduction of his bride ; for the courtship of these insects 

 is conducted in a most peculiar way. With his claspers 

 the lover seizes his betrothed by the neck, and the two 

 then fly about in line, one behind the other, tandem-fashion, 

 ever and anon dipping down towards the water till the 

 lady's tail just touches the surface, then darting up again 

 to resume their social flight. 



When at rest, the wings are either spread out hori- 

 zontally, as is the case with the larger and stouter-bodied 

 kinds, or folded up over the back like those of a butterfly, 

 as with the smaller and more slender-bodied ones. Amongst 

 the larger species, an individual will often manifest a 

 remarkable predilection for some particular twig as a place 

 of rest, and notwithstanding repeated disturbances and 

 dislodgments, will persistently return to that small perch, 

 which seems to stand to it in place of home, though, so far 

 as the ignorant human biped, who is evidently no con- 

 noisseur in such matters, can judge, there are plenty of 

 others all round that seem equally well adapted for the 

 purpose. Here, however, the creature sits, motionless as 

 death, with its body placed at an angle with the twig, till 

 the spirit of adventure again seizes it, when it suddenly 

 darts ofi" on its dashing career, ever seeking whom it may 

 devour. Dragon-flies feed upon all sorts of insects that 

 are found in such numbers in the neighbourhood of water, 

 easily catching and devouring their prey on the wing. 

 Their voracity is great, and their appetite not easily satis- 

 fied, and in consequence they are favoured with a degree of 

 longevity greatly in excess of that of the rest of the 

 Neuroptera. On the continent and in America prodigious 

 swarms are sometimes observed migrating from one district 

 to another. Each swarm consists of insects belonging to a 

 single species, and so vast are their numbers that they 

 sometimes take many hours to pass a given spot. Pre- 

 daceous and courageous though they are, while thus 

 migrating many fall victims to the attacks of insectivorous 

 birds, which pursue them, nothing daunted by their 

 numbers. A tropical species of bee-eater is said to line its 

 nest with the wings of dragon-flies. 



(To !)e confirmed.) 



E.1EATUM.— Colamntwo.p. 443, "Table of Elements": — "Earth's 

 Daily Motion in E.A., 34'13"5," should have been " Earth's 

 Hourly Motion in R.A., 34'-13"-5." 



It is proposed to establish a memorial to Dr. Rabbeth, who lost 

 hia life in attempting to save a child suffering from diphtheria, at 

 the Royal Free Hospital, on Oct. 20. Any who may wish to express 

 their practical appreciation of the brave and gallant conduct of 

 this most worthy and lamented young member of a noble profes- 

 sion, can send their subscriptions to Dra. Cromon and Hayes, or to 

 Mr. T. S. Short, at King's College. 



THE WORLD'S FIRST MERIDIAN. 



By Richard A, Proctor. 



DESPITE the opposition of the French, Brazilian, and 

 Haytian astronomers (a rather singular combination), 

 the meridian of Greenwich has been adopted as the astro- 

 nomical and geographical reference meridian for the world, 

 and hereafter we may expect uniformity to prevail in maps 

 and charts, in nautical almanacs, and in tables of reference 

 alike for terrestrial and celestial computations. Of course, 

 there will be no noteworthy change in the ordinary mea- 

 suremeut of time in difierent countries or cities. At New 

 York and Washington, for instance, where when it is noon 

 in England it is only about seven in the morning, and only 

 seven in the evening when it is midnight in England, they 

 will not, because of the adoption of the Greenwich meridian, 

 call it noon or midnight when the sun gives them so dif- 

 ferent a time of day. Ordinary or civil time will always be 

 reckoned pretty nearly by the sun — not exactly, of course, 

 for the simple reason that in that case every journey east 

 or west would involve a change of clock time. Just as 

 Ireland has a difierent time from England, not because of 

 any native cantankerousness on either side of St. George's 

 Channel, but because the sun gives different hours, so in 

 the United States they must have their clocks and watches 

 agreeing tolerably well with the sun, and so must have 

 difierent local time from ours. In difierent sections of the 

 States they will have, also, times differing by a full hour — 

 earlier and earlier for more and more westward sections — 

 an arrangement by which no place will have time much 

 more than half-an-hour different from sun time. Half-an- 

 hour is not a matter of any great importance, as we may 

 know by the fact that no one in the business of life 

 recognises the circumstance that sun time changes by 

 more than half-an-hour in the course of each year in every 

 psrt of the world. If we set a perfect clock or watch — 

 that is, one steadily recording day after day '2i true hours 

 of mean time, so that at the end of a hundred years or 

 more it would be as near sun time as at the beginning 

 — to show 12 noon when the sun was exactly south in 

 February, then, tested by the sun, that clock would seem 

 half-an-hour wrong at solar noon after about half a year 

 had passed, which would seem to show that in a year it 

 would be an hour wrong, and in six years would show six 

 o'clock at 12, and in twelve years would show 12 noon 

 for 12 midnight. Yet the discrepancy would be entirely 

 due to a want of uniformity in the sun's motion, to which 

 none except astronomers pay the slightest attention. In 

 like manner, in the United States there are places where, 

 judged by the sun (even when he is with the clock at 

 Greenwich), the clocks seem half an hour too fast or too 

 slow on the average all the time ; yet business goes on 

 undisturbed. The same arrangements will continue, now 

 that the meridian of Greenwich is adopted as the reference 

 meridian, which were in vogue before, except' that possibly 

 the American hour system may be brought into corre- 

 spondence with Greenwich time instead of Washington time 

 — so that, for instance, a traveller from England to Xew 

 York or Washington would find his watch exactly instead 

 of marly five hours fast by New York or Washington time. 

 In this way the whole world may one day be divided into 

 hour zones, so that every change of time for a voyager 

 travelling westwards would be made by putting back his 

 watch exactly an hour, and every change for a voyager 

 travelling eastwards would be made by putting his watch 

 forward one hour exactly. Though, even then, at sea, the 

 present system would have probably to be retained, by 

 which each noon the approximate local noon is adopted. 



I 



