40S 



KNOWLEDGE • 



[Nov. 



<ui-h reader has cTer boon in ihoso cliincs, will come homo to him 

 i< mo«t wondrrful word pictures. 



Your corrr«|Hiiii)ent John GrocnfipUI falls into the common error 

 of «Dpi<osinf: that Jtiebua wanted to delay the sun's .«e((inc7, wherea-i 

 he mllr commanded it not to rise, or r.»ther that clouds should 

 ■Iwcorv its rays, nntil he had completed the night sliiughter of the 

 «-nemy. ' Percival A. FoTHKKiiii.i.. 



[Thia last is outside science, however. — Ed.] 



CXIVEUSITY OF LONDON. 



[637]— I would strongly recommend "Matriculating Student" 

 (GW) to study all the subjects (to the extent required) thoroughly. 

 A specious fallacy in the policy of study is to make the probable 

 rvqairements of the examination-day the measure of necessary 

 attainments. For books of study, lieddes' " tireek (irammar,'' 

 Dalzel's "Analecta C!rax-a Minora." Xewth's "First Book of 

 Natural Philosophy," and lioscoe's " Elementary Chemistry," if 

 ihorooghly mastered, prove more than sufficient. King's College, 

 London, is one of the best teaching institutions for the examination. 

 Fk.\nk p. Montd. 



[628] — There is a very good Matriculation Examination Class 

 held at St. Bartholomew's Hospital. Mediccs. 



BRAIN TUODBLES. 

 [629] — May I add my quota to singular experiences of this kind. 

 When tired, or not feeling "fresh" at my work. I find myself 

 sometimes writing "b" for " p," "d" for " t," " v" for "f," and 

 viee rers'i. Thus I Icok over a page and find " dorifed " for 

 "derive<l," "fcntnre" for "venture," "abart" for "apart." Ilns 

 this confusion been experienced by any of your ro.iders ? 



(i. R. W. 



INTELLIGENCE IN FISH. 

 [630^— The following, which I have just received from a relative, 

 will, I think, show that minnows, small though they be, are not 

 utterly devoid of reasoning ]>owcrs : — A minnow was put into a 

 bowl which was usually only inhabited by another minnow smaller 

 than itself. Shortly after, the larger minnow was observed driving 

 the smaller one furiously and unceasingly round the bowl, and was, 

 in conie<|uenee, taken oat and put into a cup of water. Soon after 

 this, it was found that it hud jumped out of the cup and was lying 

 on the floor in an almost dying condition. It was however re- 

 placed in the cup and afterwards again transferred to the bowUvith 

 the other fish, where it has now become as lively as ever, with this 

 difference, that it now always backs away from' the little fish as if 

 afraid of it. Perhaps its fishy brain connects its frights and advcn- 

 toies with the little one, and imagines it to be its victor. 



E. T. C. W. 



A QUERY. 

 [631] — Will any of your cnrrespondents give the formula used 

 at the Meteorological Office for the reduction of barometric obser- 

 vations to lea-loTcl and to 32f F. ? Jas. Wat.so.n, jux. 



LEAP COPYIX(;. 

 [632] — The article on " Leaf Copying," by J. F. Roberts, in your 

 Isaac of the 30th ult., has interested mo very much. There is only 

 one thing about which I am a little in doubt, and about which! 

 ■hoold be glad of a little explanation. What is meant by copying- 

 paper ? It can hardly be the jjaper upon which wo take press 

 copies of onr letters, as that is never, so far as 1 am aware, ruled. 

 If you can give me this information in a future number of K.\ow- 

 LtDCE, I shall U- much obliged. 1!. K. 



IIOLSE-FLIES (■• Inde cl 'i<i<,-). 



[6*3]— Allow me to ask, throngh your columns, if you or any of 

 your reader* can tell me wliat Ucomes of the hosts of flies which 

 we sec in the sommer time, and which disappear sometimes in a 

 day or two with change of weather. Many of these insects, we 

 know, creep into the cracks and crevices of our houses, during the 

 autumn and winU-r, hybcmate, and rome forth with the return of 

 warm weather in their former mature condition. These, however 

 comparatirely few in number, do not account for our midsummer 

 • warn ,«, 



I ■h.rtild b... glail to learn whether the common house-fly is pro- 

 dnoe«l fr»<m ova, or wheth.r it is developed within the body of the 

 matenial fly into the maggot stagi-, as occurs with the bluebottle ? 



M. U. 



ansituns; to Coiifgponlitmsf* 



for tht Editor requiring tarly attention ehotitd reocA tha 

 OJIct OH or b^ore the Suturjai/ preceding the current ieeue of Knowlbdos, the 

 inereaeing circuUttion i^fvhich compete ue to tjotoprese early in the veek. 



HiSTS TO CoBBSsrOHDSHTS.— 1. Xo quettione aekinq for tcient{fic information 

 can be anevered through the pott. 2. ttttere tent to t'he Editor for eurreepondents 

 cannot befortearded, nor can the mimea or addretaea of correapondenta be given in 

 anawer to private inquiriea. 3. Correapondenta ahouldvriie on one aide only qf the 

 faper, and put dravinga on a aepnrate teif. 4. Each letter ahould have i ■" 

 •■ replying to a tetter, r^^froice ahould be made to ite numbr 

 a;>peuri, and i<< litU. 



I on Kh'ieh it 



T. A. The effect of condensation is measurable, and greatly falls 

 short of that necessnry to produce the intenRo light. On the other 

 hand, the heat required to effect dissooiation and given out when 

 chemical combination takes place is also measurable, and is found to 

 bo equivalent to that necessary to produce the light. Tliis being 

 so, can we doubt which is the true theory ? -S. M. A very singular 

 coincidence. — -Vn Admikkr of K.nowleuge. Wo wished to insert 

 your letter. But it is not quite fair. You S]ieak of Z wishing to 

 torture prisoners that his own corns or toothaches may be cured, and 

 apply the same sarcasm to Tyndall and Huxley. I doubt if any advo- 

 cate of vivisection has ever thought of getting cures for his own pains. 

 J. W. William.s. I suppose there would be a slight difference in 

 favour of the stronger-haired teazels. This would tell in the long 

 run, though many even of these would doubtless bo consumed. — P. O. 

 Donn. Please address the publishers on such matters.— M. H. 

 C. — " Gradatim " was asking about the actual glacial periods, 

 not about relative glaciation. The quotation is given as a line, not 

 as a hexameter; if it had been given as in Horace, the passage 

 would have been absurd. It would have read thus : — British earth- 

 quakes remind us of the old line, " the mountains are in labour, a 

 ridiculous mouse tcill be born," where we meant " is bom." That 

 would have been absurd if you will. It was actually to show that 

 the original was not quoted from that the order of tlio first two 

 words was changed. — Edm. P. Toy. The calculation is given in my 

 " Satnrn and its System." But 1 may shortly give it again hore. — 

 Tbesilian. I am somewhat of your opinion, but originally the 

 papers were to have been fewer.- J. M. S. That quotation ap- 

 peared in our first number. It sounds a little too assumiuR- 

 for a quotation at the head of our correspondence. — Th. I). 

 Many thanks. We had cut out that passage for (luotation, 

 but had not room. There is more to tho samo effect, 

 in this month's " G. Mag." May quote some of that. — 

 Gkub. What a charming nom deplume ! Tho invisible vapour of 

 water turns into visible cloud under both conditions. In my 

 article on Fog in Rodwell's " Cyclopaedia of the Physical Sciences," 

 I wrote, "Thus a river flowing from a warm to a cold region, wilt 

 often be covered with fog, lipcauseitis colder thnn tho surrounding 

 air, which, becoming cooled below tho dew-point, discharges il.s 

 moisture in the form of fog ; but again, a river flowing from ;i 

 warm to a cold region will also often be cov<'red with fog, because 

 it pours more vapour into the air than can be retained in the invi- 

 sible form." This last corresponds with tho case in your experi- 

 ment. —J. M. I wish you had rei)ea(ed your signature ; had to 

 search for former answer. The locus is the env(lo])e of a series of 

 circles of equal radius, all having their centres on tho ellipse. To 

 obtain tho equation to this envelope would imt be a very simple 

 matter, simply because the equation is one of a rather high order. 

 You get a biquadratic equation, involving the X-coordinato of the 

 original ellipse ; and eliminating this (as, of course, also (lie Y'-cn- 

 ordinato) you get the equation required ; but what you c an du willi 

 it when you have it I do not know. — Rev. U Itii. S. You mistake ; 

 our omission of religious matter means only that controversial 

 matter is excluded, not that " (iod cannot bo introduced into his 

 works." You will find no such omission either in KNOWLKriOE, or in 

 the works of (he writers attacked in il- i. .|.. r !■,.■ .■.■usiircd. Wedid 

 not ridicule this hi'it, tho case being I ; .: !■ i i i ijcule.-- C. W. 



BontNK. W..hnpcthatCol.KeyBerm!.', I ;,..,,, i !,,■ mie account 



of wlmthc.ll.l.aiidso.-urrecttl.cubKn,.: ,, , - :,! Al,i,l, have been 

 goingthe rniir,-l .,lij.- |.;i|.m I. ■ i 'I -pace for the 



simple ge<M , I i , ..i 1 1 ,ii . , r , | ■ I,,, circle is loss 



than3}. Uli. im ! n I rn.ia-e exceeds 



ai; see l)c M-.i' u,' ■ l;,M. w .,1 I',,, , ... ,, i 1 7, -A. B. You 

 have gotten a lifllc irjixcil. (lur fcii-riiula cuniicctH /■ and a, tho actual 

 and the mean distaneo ; from it and a known perihelion velocity, 

 you seek to obtain tho earth's perihelion distance — a most illegiti- 

 mate proceeding! Thp ratio 207 : 208 which comes out is really 

 the ratio between the estimates of the sun's distance used by mp 

 and you respectively. — A. P. Osiioitxi:. I know of no good text- 

 book of astronomy for beginners- those by astronomers who knon' 

 are so unintelligibly written, and those well written are so obviously 

 written by those who do not know. We speak, be it noted, of text- 

 books only. In Lardner's Handbook you will find a pleasing 



