March 10, 1882.] 



KNOWLEDGE 



411 



stdod when we think of the ease mth which air can be drawn into 



:iTiil oxiu'lled from it. The lunjfs are to bo rei^arded as elastic baf^s 



wliich :ii'i' not connected with the walla of the chest, both they and 



th" walls being covered with a smooth membrane called the pleural 



mlrane (wh ch, when inflamed, produces pleurisy). Now, the 



ice (or rather separation, for they aro nominally in contact), 



'i tween the two layers of pleural membrane, is air~ii'jht, so that 



u lien the chest cavity enlari^es (by movement of ribs and descent 



c'f midriff, or diaphra^^m), the elastic lanp;3 follow its walls, and so 



ail' mshcs in through the wind-pipe to fill the largar space so pro- 



tiuced, and we are said to inspire. If, however, a hole be made 



into the space (or separation) between the lungs and chest wall, 



then, of coarse, when the chest cavity enlarges, the lungs will not 



|iand, but air will simply rush in at the hole that has been made. 



It the space between one lung and the chest-wall is quite distinct 



1 tn that between the other lung and the chest-wall, so that if only 



• ■:ie be opened into, the man still lives and breathes with his other 

 IiiHg; but if both spaces be opened into death must at once occur. 

 Now, the heart is, as it were, quite distinct from these air-tight 



ices, so that if a hole exist (as has been known in certaiii cases) 

 1 'Ugh the chcst-wall opposite that organ, it will not open into 

 I Nor of tlie spaces, and so will not interfere with breathing. — 

 I . VV. G. 



,268] — PnoTOGB.iPHY.— " Anon " has need to be careful in 



meddling vnth photography. It is an expensive pastime. For 



r.eral work (landscape and portrait) consult Abney's " Instruc- 



M3 in Photography" (2s. 6d., Piper & Carter), or Hughes' 



l'liotogra])hy " (Is., Simpkin). If only for portraits, Heigliway's 



I 'tactical Portrait Photograph" (Is., Piper & Carter) will best 



:: him. Full instructions and chemicals required are given in 



vo works, and the advertisements will indicate where to get 



lintn. The "cheapest articles" are not to be advised. Failure 



and disgust are sure to follow the use of cheap and necessarily 



nasty articles. Better give a higher price and get a good article. 



I f it is intended to use dry plates, Eder's ' Modern Dry Pltites " (.3s., 



I tliink, published by Piper A- Carter) will be useful. — F. M. 



260] — Carbonic acid was shown by Calvert to be necessary to 



• rusting of iron, besides oxygen. Sea-water contains more car- 

 ric acid than average fresh water. — C. T. B. 



277] — Balmain's luminous paint is calcium or barium sulphide, 

 1 le by heating either gypsum or heavy-spar with coal. — C. T. B. 

 285]— SciK.NTiFic Terms. — " Prestcr W." will find Dunnian's 

 Mossary" (Griffiths & Farran), a useful book for "Biological, 

 Anatomical, and Physiological Terms." — Chas. W. Duckwokth. 



:W0].— The question of " G. G. D.," Xo. 300, p. 388, is a very 



* ir one. Assuming that the evaporation from the damp surround- 

 -s have saturated the warm air inside the room, a condensation 



naif its vapour would certainly take place if it were reduced from 



to 32° without any interchange with the outer air, i.e., if the 



ni were air-tight and cooled exclusively by conduction through 



walls. The damp surrounding would then simply recover all 



• moisture they had previously supplied to the warm air. If, on 



■ other hand, the doors and windows were thro^vn open, and the 

 ni were rajiidly cooled by an exchange of cold air from outside, 



• walls would continne for some time warmer than the incoming 

 ■. and therefore would receive no deposition of moisture from it ; 

 t on the contrary, would communicate some heat to it, and thus 



!'. e a drying action. I have imagined these opposite extremes as 

 exaggerated illustrations displaying the principles. Practically, 

 however, a mixed action occurs. Conduction takes place through 

 the thinnest element of partition, the -window glass, and there wo 



■ an abundant formation of what I may venture to call domestic 

 V. Besides this, an interchange of atmosphere slowly takes 

 " e ; but not more slowly than the cooling of the walls. Under 



th 'se conditions, the condensation of excess of vapour is limited to 

 til" window panes, and the brick or stone walls, Ac, remain dry. — 

 \V. Mattif.c Williams. 



fyetter 220] — Health of Navvies. — Edwin Sachs (p. 325), in 

 ' ly to my letter on the above (p. 254), says that the "natives" 

 lying by thousands in Java, Ac, from fever " though inveterate 

 ['■I chewers." It would have been more satisfactory if Edwin 

 Sachs had informed the readers of Knowledge whether the fever 

 was indigenous or not, as this would, of course, make all the dif- 

 ference, and would account tor the, at present, remarkable fact of 

 the " natives being more easily affected by fever than aro Euro- 

 peans." If Edwin Sachs will read my letter again, he will see that 

 I was alluding to fevers, &c., incidental to marsh life. Mr. A. H. 

 Church, in his edition of " Johnson's Chemistry of Common Life," 

 never intended the betel nut to be used as a preventive against 

 fevers which contact with foreigners may have introduced. — 

 F. C. S. 



Sliistorrd to CorrtJ^pontentsJ. 



Office < 



•All I 



mmiim.aliaiit fur Ihr Editor rrqiiiriii} ear!) al/riilion ihould reach I' e 

 li^ore the Saturday preceding the curreitt ueue of Kxowlbdob, tJ.e 



rculatton of vhwh LOmpeh ua to go to preta early in the week. 

 Hints to Cohhf.shosdkxts.— 1. No qiieatioxt atkirtii fur icienlific in/ormitioi 

 can be anaic^eil through the pout. "i. heltcre aeni to the Editor for correapondentt 

 cannot be foncnrded ; nor can the namea or addreiiea of correapjndenta be given in 

 anewer to private inijniriea. 3. No queriea or repliea aacouring of the nature of 

 adcrrtiaementa can be inserted. 4. Lettcra, queriei, and rciiliea are inaerted, unleaa 

 contrary to Itnle 3, />.■« of charge. 5. Correapondeala ahould vrile on oiK tide 

 only of the poper, and p'lt dravinga on a aepara/e teaj. 6. Each Utter, query, or 

 reply ahontd have a title, and in replying to leltera or queriea, r^erence ahottld be 

 rt-ide to the number of letter or query, the page on which it appeara, and ita title. 



Wo 

 but 



Mark H. Jidge. Thanks for report of Sanitary Association, 

 but readers would not allow us to insert so much in way of 

 report. — E. Luxmoobe. Many thanks for description of compound 

 pendulum, which shall shortly ajjpcar. The curves are very inte- 

 resting. Is there no ink, either black, scarlet, or orange, which 

 could be used? If there were, the curves could be photozinco- 

 graphed. — Cogito. When, in No. 11, I spoke of the ecliptic or 

 plane of earth's path as unchanging, I meant that if an observer 

 were supposed to watch the earth from the sun's centre, her 

 apparent course among the stars would be unchanging. Tlte 

 earth's polar axis remains inclined at almost an unchanging 

 angle to the plane in which the e.-irth travels, just as the 

 axis of a spinning top is inclined at almost an unchanging angle to 

 the horizon plane, but this axis varies in direction (also as the axis 

 of a reeling top varies) and the plane of the equator, which is 

 always at right angles to the earth's axis, of course varies with it. 

 Refer to the same figure p. 219, Xo. 11 ; here EE conosponds with 

 the earth's equator. It remains always inclined at the same angle 

 to the vertical, but reels round as the globe spins. I have not jet 

 done with precession, but every week I get some such message as 

 this : " We have forty-seven columns of over -matter, and two, 

 three, or four more pages of advertisements than we can get in 

 without displacing something. What aro we to do ? " and I have to 

 reply. Keep out my article on comets, or on precession, or on the 

 Pyramid, or Foster's articles on illusion, or articles by some 

 one else who is willing (I know) to wait. — J. K. Campbell. 

 should have liked to use your paper on the Slide Eule, 

 what can we do ? A wants more about microscope ; B more 

 about chemistry, C botany, D entomology, B says turn out whist, 

 and have in mineralogy, F says we want no chess, but would like 

 something about pottery, G would like more biology, H palaeontology, 

 J says " All work and so little play makes Knowledge dull to day. 

 Why cut down whist and chess to a column each ? " and so on, to Z. 

 You catch the idea ? — M. Hill. Neither drawing represents the real 

 changes of the moon's apparent position. If you attach a circular 

 disc to a celestial globe, set to latitude of London, and caiTy the 

 disc round from horizon to horizon, you will see the real changes, 

 and also why they occur. A gas is said to be in the critical state 

 when the pressure and temperature are such that, if the latter 

 were in any degree lowered, the gas would liquefy. — F. W. B. 

 Bouvekie. Fear we could scarcely find room in Knowledge just 

 now for papers on philological subjects. — J. H. Fallon. Know 

 nothing about the Society for the Promotion of Scientific In- 

 dustry. — W. B. Are not — 3 and — 2 as obviously roots of 

 the modified equation ? — S. Stanier. Power cannot be 200, if 

 Jupiter had at the time of observation ajiparent diameter 45". 

 Three days before date of your letter, Jupiter's diameter was only 

 36". — Private Student. Your examples aro rather too common- 

 place to be dealt with in Mathematical Column. (1.) The equa- 

 tions to lines parallel to i/ =m .t -I- b, and at distanc e a from origin 

 (rectangular co-ordinates), are y=-mx±.a^ i + m'. (2.) If AB is 

 parallel to x cos. a + y sin. a=p, and OA.UB = c', equation to AB is 

 ,T cos. a + y sin. a = '^ ^'°1° . (3.) If -iU be parallel to y = mx + J> 



•^^tan a 

 and 0.4 + 0B = <-the equation to .IRis ;/ = )».■ -(- 



1+7,.. 



really must not ask such questions as those ; you mistake the 

 purpose of Knowledge in doing so. — Historian. Your questions 

 hardly suited to a journal of popular science. Considering how 

 those two historians have denounced each other, it would be un- 

 wise of us to pretend to decide between them. — W. A. S. Your 

 reply states the matter clearly, but does not explain. Mesmerism 

 may be " nerve force producing artificial somnambulism on a suscep- 

 tible subject." But why ? or (if we cannot have Why) how ?— J. W. 

 Wood. Your reply scarcely explains much. — H. W. B. Thanks; 

 but fear the merely verbal contest you invite would be of small 

 benefit.— Geo. St."Clair. The star Alpha Centauri ; moreover, 

 this is the only first magtjitude star which ever has shone in the 

 direction of the Southern passage. The Great Bear was regarded 



But vou 



