Nov. 18, 1881. J 



KNOWLEDGE 



48 



AN II 



ilRATED 



Q 



MAGi^ZINEOF^IENCE 



Pi. AlNtWORDED -£XACT&i)ESCRIBED 



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LONDON: FRIDAY, NOVEMBER 18, 1S8I. 



CONTENTS. 



Solids, Liquidi, and Gasos.— Part I. 



By W. Mattieu Williams 43 



The Philosophy of Animal Colours. — 

 Part II. By Dr. Andrevr Wilson, 



F.R.S.E 4* 



Brain Troubles. — Impaired Memory 45 



Intellicencein Animals.— Part n -16 



Are Women Inferior to Men? 47 



Comets' Tails. By the Editor— (/«»»- 



trated) ". 48 



Reviews :— The Great Pyramid Mea- 

 Porcs, and the Diameters and Dis- 

 lances of the Sun, Earthj andMoon. 



PAGE. 



Br Joseph Baiendell. F.R.A.S. ... 50 

 NenModeofGrowing Plants. BvE.C. 51 



X Planet Outside Xeptune 52 



CoBEEspoxBEycE. — Error in com- 

 puting Periphery of Ellipse — 

 Comets — Figures of the Conic Sec- 

 tions — Waste of Solar Heat, &c. ... 55 



Queries &) 



Replies to Queries 60 



Our Mathematical Column 61 



Our Whist Column 61 



Our Chess Column '.63 



Answers to Correspondents 64 



SOLIDS, LIQUIDS, AND GASES. 

 By W. M.vttieu Willlois, 



TART I. 



THE gi'owth of accurate knowledge i.s continually nai'- 

 rowiiifj, antl often obliterating the broad lines of 

 •distinction that have been drawn between different classes 

 of things. I well remember when our liest naturalists re- 

 .^arded tlieir "species'' of plants and animals as fundamental 

 and inviolable institutions, separated by well-defined boun- 

 dai-ies that could not be crossed Darwin has upset all this, 

 *Ed now we camiot even draw a clear, sharp line between 

 the animal and vegetable kingdoms. The chemist is even 

 crossing the boundary between these and the mineral 

 tingdom, by refuting the once positive dictum that organic 

 su'bstances (i.e., the compounds ordinarily formed in the 

 course of vegetal)lc or animal gi-owth) could not be pro- 

 duced directly from dead matter by any chemical device. 

 Many of such organic compounds have now been made in 

 the laboratory from mineral materials. 



We all know broadly what are the differences Ijetween 

 solids, liquids, and gases, and, until lately, they have been 

 very positively described as the three distinct states or 

 modes of existence of matter. Mr. Crookes suggests a 

 fourth. I will not discuss this at present, but merely 

 consider the three old-established claimants to distinctive 

 existence. 



A solid is usually defined as a body made up of particles 

 •which hold together rigidly or immovably, in contra- 

 distinction to a fluid, of which the particles move freely 

 over each other. "Fluid"' is the general term including 

 both gases and liquids, both being alike as regards the 

 mobility of their particles. At present, let us confine our 

 attention to liquids and .solids. 



The theoretical or perfect fluid whicli is imagined by the 

 mathematician as the basis of certain abstract reasonings 

 has no actual existence. He a.ssumes (and the assumption 

 is legitimate and desirable, provided its imaginary character 

 is always remembered) that the supposed particles move 

 upon eacli other with perfect fi-eedom, without any friction or 



other impediment ; but, as a matter of fact, all liquids exert 

 some amount of resistance to their own flowing ; they are 

 more or less viscous, have more or less of that sluggisliness 

 in their obedience to the law of finding their own level 

 which we see so plainly displayed by treacle or castor oil. 



This viscosity, added to the friction of the liquid against 

 the solid on which it rests, or in which it is enclosed, may 

 become, even in the case of water, a formidable obstacle to 

 its flow. Thus, if we make a hole in the side of a tank at 

 a depth of 16 feet below the surface, the water will spout 

 from that hole at the rate of 32 feet per second, but if we 

 connect with this hole a long horizontal pipe of the same 

 internal diameter as tlie hole, and then observe the flow 

 from the outlet of the pipe, wo shall find its velocity 

 measural.)ly diminished, and we shall be greatly deceived if 

 we make arrangements for carrying swift-flowing water 

 thus to any great distances. 



Three or four years ago an attempt was made to super- 

 sede the water-carts of London by laying down on each 

 side of the road a horizontal pipe, perforated with a row of 

 holes opening towards the horse-way. The water was to 

 be turned on, and from these holes it was to jet out to the 

 middle of the road from each side, and thus water it all. 

 I watched the experiment made near the Bank of England. 

 Instead of spouting across the road from all these holes, as 

 it would have done from any ow of thcni, it merely 

 dribbled, the reason being that in order to supply tlieni all, 

 the water must run through the whole of tho lo\a pipe 

 with considerable velocity, and *\\h viscosity and friction 

 to be overcome in doing this nearly exhausted the whole 

 force of water-head pressure. Many other similar blunders 

 have been mide by those who have sought to convey water 

 power to a distance by means of pipes of such diameter a-s 

 should demand a rapid flow through a long pipe. 



The resistance which water ofl'ers to the stroke of the 

 swimmer or the pull of the rower is partly due to its 

 viscosity, and partly to the uplifting or displacement of 

 some of the water. If it were perfectly fluid, our move- 

 ments within it, and those of fishes, itc, would be curiously 

 different, and, in fact, the whole face of this globe would 

 be strangely altered in many re.spects. I will not now 

 follow up this idea, but leave it as a suggestion for the 

 reader to work out for himself, by consiilering w'hat would 

 remain undone upon the earth if water flowed perfectly, 

 without any internal resistance. 



The degrees of approach to perfect fluidity vary greatly 

 with different liquids. 



Is there any such a thing as an absolute solid, or a body 

 that has no degree of fluidity, the particles or parts of 

 which ^vill admit of no change of their relative positions, 

 no movement upon each other without fracture of the 

 mass? This would constitute perfect riijidity, or the 

 opposite io fluidity. 



Take a piece of copper or soft iron-wire, about one-eighth 

 of an incli in diameter, or thereabouts, and bend it back- 

 wards and foi-wards a few times as rapidly as possible, but 

 without breaking it ; then, without loss of time, feel the 

 portion that has been bent. It is hot — painfully so — if the 

 e.xperiiuent is smartly made. How may this be explained ? 



It is e\-ident that in the act of bending there must have 

 been a displacement of the relative positions of the particles 

 of the metal, and the force demanded for the bending indi- 

 cated their resistance to this movement upon each other ; 

 or, in other words, that there was friction between theni, 

 or something equivalent to such intemp,l friction, and thus 

 the mechanical force exerted in the liending was convert^'* 

 into heat^force. 



Here, then, w^s fluidity, aooordiu^ ♦-^ "' ^ 



tion : not perfect fluidity, b--^ .. tJie above defiui- 



-.. fluidity attended with 



