208 



• KNOWL.EDGE ♦ 



[Jan. 6, 1882. 



of a more or lemi nearly-circular form. Encli of these cai'itieB con- 

 tained water nnd n bubble (of attenuated ntoam, 1 suppose) ; some 

 of these bubbles remained in the centre of their colls, but others 

 aoon (e»i>eciiilly if the sun was hot) bcf^un to mo%-e round their 

 cells, sometimes in jerks, at others smoothly, occasionally oscillntin^j. 

 I should be plad to know why I woa unable to see the branchlcts, 

 and should be greatly obliged to any reader who would explain the 

 cause of the little bubble's curious movements. 



Enclosed 18*8 drawing which will give a good idea of what I 

 observed. The larger discs represent the cavities containing 

 liquid, while the small circular black and white spots are the 

 bubbles. E. C. R. 



DIFFICULTY OF OBTAINING " KNOWLEDGE." 

 [168] — Having experienced the same diflSculty as mentioned by 

 your correspondent in No. 7, I would recommend your would-be 

 readers to order Knowledge of their newsagent, insK'ad of the 

 bookseller, who, for some reason best known to himself, professes 

 ignorance of the publication. — I am, Sir, yours faithfully, 



A. Gacbert. 

 [We have received several letters to the above effect. — Ed.] 



[169]— In reference to Letter No. 134, page 144, the fact that I 

 have generally obtiiined Knowledge from my bookseller in North 

 Shields before 9 a.m. on Friday mornings may convince Mr. Arm- 

 strong that either his booksellers or their London agents arc alone 

 to blame. — Tours, Ac, Geordie. 



" OUE UNBIDDEN GUESTS." 

 [ 170] — Surely " the great lesson to be learned " from Dr. Andrew 

 Wilson's frightful disclosures in the last number of Kxowxedge, 

 respecting tapeworm and trichinoe, is ouo iiuite different from that 

 proposed by him , and not " thorough cooking," but total avoidance 

 of the substances liable to be infested, is the true and sensible 

 remedy. From the " Perfect Way in Diet," recently favourably 

 noticed by you, it would appear that man is, by his constitution and 

 structure, not carnivorous at all, but becomes so only through 

 degeneration of habit. From this it ought to follow that man can 

 attain to the perfection of his nature only by subsisting on the sub- 

 stances indicated by his structure. My own experience favours 

 this conclusion. Having abstained fron\ llesh-food for some seven 

 years, I find the results — physical, intellectual, and other — such as 

 to make me regret that I was not a follower of the " Perfect Way " 

 from the first, and my experience is by no means a singular one 

 within my own circle of acquaintance. — Yours, &c., E. M. 



THE POLE STAR AND PRECESSION. 



[171] — In your promised paper on the Precession of the Equi- 

 noxes, can you give us a star-map, showing the circle described by 

 the North Pole, and therefuro all the stars which have been suc- 

 cessively Pole-stars ? One meets with the statement that about 

 4,000 years ago n Draronis was the Pole-star ; but no full informa- 

 tion is given in popular books. With such a star-map as I suggest, 

 we could find for ourselves the Pole-star for any period of the past. 

 — Yours, Ac, Geobck St. Clair. 



[Will supply such a map the week after next. — Ed.] 



A NEW COMPARISON OF POISONS. 



[172] — Notwithstanding your approval of "Technical Chemist" 

 (Letter 102, p. 116), I venture to think be i« not quito right. The 

 allegation is that li. cc. is three times as poisonous as ba. ce. ; and, 

 while admitting that ba. ce. is poisonous, it is urged that li. ce. ia 

 often prescribed in comparatively large quantities for gout. Now, 

 why mystify M. Richet's plain proposition? Li. ce. has 20 per 

 cent, of metal, where the citrate has probably much less than 7 per 

 cent. ; liesides, iron and mercury may be very poisonous in one 

 form of combination, and very innocuous in another. S. E. P. 



SOUND. 



[173]— "C. T. B." (query 60, p. 125) may', be right in saying 

 " the lighter the weight, the better does a body transmit sound ' 

 but only in conjunction with a mysterious function of elasticity, 

 which figures so largely in scholastic formulae and ideas. We know 

 that air transmits sound in round numbers, about 1,000 ft. per 

 second ; water 4,000 ft. ; and some dense woods and metals, 10,000 

 to 15,000 ft. per second. A great chemist on the Continent is 

 holding up to ridicule a kind of weekly anthology of modem 

 chemical utterances ; with some sueh feeling I would try to fairly 

 paraphrase the sound contentions of '* T. J. H." (query 14, p. 123). 

 The condensation augments the elasticity by the heat generated in 

 the condensation of particles. The rarefaction augments the elasti- 

 city by the cola generated, and also by the separation of particles. 

 The heat generated remains there to increase the velocity. It is 

 because the heat generated in the condensation augments the rapi- 

 dity of the condensation, and the cold developed, augments the 

 rapidity of the rarefaction, that the heat and cold both help to 

 augment the velocity of the sound wave. Eolecticvs. 



THE MAGNETIC NEEDLE. 



[174]— Tliere is no attraction of the kind " W. H. P." (query 90, 

 p. 123) seems to suppose. The affection is one rather of polarity 

 or deflection. Let "W. H. P." imagine a globe with convolutions 

 of wire conveying electricity round the equator, representing atrtual 

 earth currents, then he will find that particles of air or iron will 

 have a binarj- polarity induced in them, at right angles to the 

 direction of current. There will be a field of magnetism where 

 the lines of force point N. and S., or to the two poles ; but there 

 is no tendency to movement or change of position of the polarized 

 medium. 



N 



ma 



^ 



_> 



In order to remove any ambiguity about these poles, it may be 

 well to explain that this same field of force subsists all round any 

 wiri- conveying a current. Here, then, we have a circular field of 

 force with no poles. Let (a) be a section»of the wire carrying a 

 current downwards or from the point of view ; then small un- 

 magnoti/.ed needles (with no directivity) would have polarity 

 induced in them such as to point east, west, north, or south, as per 

 diagram. If the current flow upwards, these polarities would be 

 reversed. 



In very many cases, arrows indicate motion or a tendency to 

 motion. In this case, they only convey the idea of polarity in the 

 media, where iron is immensely more sensitive or conductive than 

 air. Eclecticcs. 



BUTTERCUPS— BEES AS FLOWER FERTILISERS. 



[175] — In answer to "West Riding," I should like to remail; 

 that where grasses, daisies, and docks predominate, I have never 

 obsen-ed that the vegetation was "thick and matted;" I was 

 alluding rather to tangled hedgerows and overgrown spaces. " Weet 

 Riding" can hardly exjicct me to explain the whole philosophy of 

 leaves, among other things, in a single short article. Oddly enough, 

 my intention, before seeing his letter, was to write a paper for 

 Knowledge on the foliage of daisies and plantains, and, with the 

 Editor's kind permission — [Gladly accorded. — En.]— I will now do 

 so shortly. The subject is one which I have long been observing. 



Mr. Dunbavand is mistaken in supposing that bees never visit 



