308 



♦ KNOWLEDGE ♦ 



[Nov, 16, 1883. 



€5 1 tonal (§055ip. 



A GREAT pressure on our space this week causes several 

 promised papers to be delayed till next week's number. 



I HEREBY return my thanks to the full audience which 

 greeted me so pleasantly on IMonday at the Town Hall, 

 Kensington. The hall is a magnificent room for speaking 

 in ; I have never known any where the management of 

 the voice was easier. Those who have not spoken 

 much in public can hardly imagine what a difference 

 the acoustic properties of a hall cau.se. Where speaking 

 is easy, the thoughts flow more readily, and all that the 

 lecturer has to do is made easier to him, and the lecture 

 pleasanter in every way to the audience. On Tuesday, 

 when I addressed a large audience in the Rink Hall, 

 Blaekheath, I felt the dirterence in a very marked degree. 

 Speaking in a long low room with a slant roof differs as 

 much from speaking in a room like the Town Hall, Ken- 

 sington, as shouting through a speaking-trumpet differs 

 from parlour converse. Imagine the effect of trying to 

 explain, reason, sketch, and in passing make light jests, 

 through a speaking-trumpet. 



I WONDER how often during a lecture I ought to state 

 that not the theory running through the lecture should 

 be chiefly considered, but the facts which the theory is 

 intended to associate together, and in some degree to 

 explain. I very carefully noted this in my first lecture at 

 Kensington, yet in the kindly notice which appeared on 

 Tuesday in the Daily Neics the circumstance is overlooked, 

 and my lecture described as though intended to advance 

 and support certain theories. 



" Let Knowledge grow from more to more."^ — Alfeed Tennyson. 



Only a small proportion of Letters received can possiltly he in- 

 serted. Correspondents must not ie offended, there/ore, should their 

 letters not appear. 



All Editorial communications should be addressed to the Editor of 

 Knowledge ; all Business com7nunications to the Publishers, at the 

 Office, 74, Great Queen-street, W.C. Ip this is not attended to 



DELAYS ARISE FOR WHICH THE EDITOR IS NOT RESPONSIBLE. 



All Retnittances, Cheques, and Post Office Orders should be made 

 payable to Messes. Wym.in & Sons. 



The Editor is not respo^isihle for the opinions of correspondents. 



No COMMUNICATIONS ARE ANSWERED BY POST, EVEN THOUGH STAMPED 

 AND DIRECTED ENVELOPE BE ENCLOSED. 



OEDXAXCE MAP MEASUEEMENTS. 



[1002] — Apparently, our retrenching Government out-parallaxes 

 "Parallax" and not only holds earth is flat, but that it is flat as 

 pancakes or paper maps, and that hills and dales are mere illusions. 



Certain officials have certain allowances when at work bevond a 

 specified distance from home. A Parliamentary Return actually 

 defines this to be " by the nearest available route," which seems 

 fair common sense. 



But " some Treasury Hampden, bom to blush unseen," has dis- 

 covered that a simpler way to measure is by a pair of compasses, 

 so that not only does the Treasury calculate these terrestrial dis- 

 tances irrespective of roads, but irrespective of ups and downs, as 

 though the people's servants could travel through air like the pro- 

 verbial crow. The official proof of the accuracy of this method 

 lies in the fact that it docks certain coins ; but as I trow even the 

 Lords of the Treasury can neither buy nor sell land on this style of 



measurement, can you tell us any other cases in which this style 

 has place ? Is it not a fact that in measuring from an ordnance 

 map a surveyor or other person skilled in map-reading takes into 

 account the contour as shown by the lines which give rising ground 

 according to their distance from each other ? Or, to put it more 

 succinctly, given two points on opposite sides of Snowdon, can the 

 distance common-sensibly be reckoned as from point to point 

 through the hill, instead of round the base or over the top ? 



E. H. O. 



.SILENT LIGHTNING. 



[1003] — I was once witness of a very exceptional case of silent 

 lightning during the day. Many years ago I was \-isiting a friend 



at the village of C , in this neighbourhood, and distant from the 



large town of D some ten or eleven miles, and which can be 



seen in ordinary weather clearly from C . Abont si.x p.m. on 



this summer evening, while the landscape in the neighboorhood of 



C was bathed in sunshine, I happened to look towards D , 



and saw a very black cloud enveloping it. In the face of this 

 cloud I distinctly saw repeated tongues of spiral-like flames, rising 

 as if from the ground, but I heard no sound. The display was very 

 magnificent, the bright flashes showing very well on the backgronnci 

 of the dark cloud. 



Next day the papers recorded that a violent thunderstorm had 



taken place at D , on the evening of the previous day. From 



this I would conclude that while the intensity of light waves is not 

 diminished by distance, that of sound waves becomes, within a 

 short distance, wholly inappreciable by human ears. Senex. 



LUMINOSITY OF PLANTS AND ANIMALS. 



[1004] — One evening some years ago, when staying near the 

 village of Shepperton, in Middlesex, a friend asked me to come out 

 to look at some kind of worm, which was giving light in the road. 

 It proved to be a centipede, like that described in Knowledge, 

 No. 104, p. 263, which is, I believe, called Scolopendra electrica, 

 and left on the ground over which it wae crawling a slightly 

 luminous trail for some distance behind it. 



On another occasion, when walking on cultivated sandy soil near 

 the seashore, I found that a number of bright spots appeared on 

 the ground wherever my feet had been in contact with it. It being 

 too dark to see what produced this luminous appearance, I care- 

 fully removed some of the soil in which were these bright spots, 

 and on washing it afterwards, found it contained a few small earth 

 worms, which, when gently touched or pressed, emitted light in the 

 dark. 



The following short extracts from Phipson's interesting little 

 book, " Familiar Letters on Some Mysteries of Nature," will, I have 

 no doubt, interest many of your readers : — 



" In 1762, Elizabeth Christine Linne, daughter of the celebrated 

 Swedish naturalist, discovered that certain flowers emit light just 

 after sunset." 



'• The plants which have been found conspicuous in this respect 

 are the nasturtium, the sunflower, various garden marigolds, more 

 especially the double ones, the two species of tagetes or Rose de 

 rinde and CEillet d'Inde, the yellow lUy {Liliutn Indbife riiyn) , and 

 the tuberose." 



"The phenomenon is seen in July or August after fine, dry 

 weather, and soon after eight in the evening." 



" It only occurs in dry weather, and is visible for about half-an- 

 hour after sunset. After a rainy day, or when the air is damp, it 

 never occurs." 



" Professor Fries observed the phenomenon on a group of poppies 

 (Papaver orientale), thxee or four flowers of which emitted little 

 flashes of light." 



" The light of these plants does not appear to be referable directly 

 to the production of electricity, but more probably to a peculiar 

 principle, that I have termed NoctUucine, which is produced by 

 luminous animals." 



"The common earthworm in October, and the Scolopendra 

 electrica, or luminous centipede, in September, are often seen in a 

 highly luminous state in this climate." 



" In all these luminous animals, the researches of Ehrenberg and 

 many other distinguished naturalists have shown the existence of 

 certain organs specially adapted for the production of light." 



" In luminous animals, these organs produce the substance which 

 I have called noctilucine. It is a fluid nitrogenous substance, very 

 easily decomposed, and which shines in the dark by oxidization, 

 just like phosphorus itself." 



" Whether it is taken from the glowworm, the scolopendra, or 

 any other luminous animal, it shows the same chemical properties 

 and the same spectrutn (from E to F)." 



" By luminous insects it is secreted as fast as required by nature 



