118 



KNOWLEDGE 



[Dbc. 9, 1881. 



tho point of intorwrtion <', rind dn tlint one of tlio two niarko on it 

 lies in tlip dcniicirrlo, nn<l tlio otlinr in AB prodnrod, nH in E nnd D 

 rcopcctivply. Thr point /> thus olilninpfl (fivcn fho (ingli< CDA, 

 whith in tho roipiircd third of AUC. Thr proof is interoating. 

 For tho exterior ani;]r\ AIIC ia — C + P. But sinro BC is " to 

 BK nnd to EP. the nnglo BCE is = to BEC, and this to 

 tBD+EVB-, that is, to twice the nnplo Z>. Therefore ABC is 

 equal to 3 limes D. — Yours, 4c., James Wabben. 



SINGULAR ILLUSION. 



[110] — A RinRulftr nnd pmr- 

 ticnl ilhistrntion of the opficd 

 illusion, FiK. 2, of Mr. Foster's 

 eamo under my notice a short 

 time ago. Tho tower-arch of a 

 church had been rebuilt, and 

 during its construction a tall 

 strut was set at an angle to 

 the base, with its head filed 

 against tho wall juat above 

 the apex of the arch. Whilst 

 KtJinding at the chancel steps, 

 tho arch presented a most 

 singular appearance, and I 

 called the contractor, who 

 liKikcd somewhat alarmed nnd 

 astonished, and we both thought 

 the arch must have dropped on 

 <mo side. Tho accompanying 

 drawing will explain what wb 

 saw. The pointed arch shows 

 better than the semicircle tho 

 apparent illusion of the two 

 lines belonging to different 

 circles. F. Long. 



In order to make the illusion 

 more plain, the strut is drawn 

 out of proportion. 



ILLUSIONS. 



[111]^A few remarks upon the paper by Mr. Foster, on " Illusions," 

 may be of some slight interest. The effects which angular, curved, 

 and straight lines, in juxtaposition, have upon one another with 

 respect to the e}e are certainly very curious, and few eyes will fail 

 to perceive the apparent distortions in the cases figured. I should 

 like to remark, however, that in Figure 5, to my eyes, and to those 

 of the one or two persons to whom I have presented the figure, the 

 effect of the curves on the straight lines is just the reverse of that 

 stated to be tho case by Mr. Foster. 



In Figure 6, to my eyes the straight lines AB and CD appear 

 nearer in the middle, and EF and GH appear farther apart in the 

 middle, thus agreeing mth what is stated, and being tho reverse of 

 the two previous pairs of lines, which is what one would expect. I 

 cannot by any method of gazing cause the straight lines in the last 

 two pairs. Figure 7, to appear anything but parallel. 



Below will be found a figure which shows the " flattened " 

 appearance of a circle at the four comers of an inscribed squaro 

 — a distortion of the same nature as that shown in Figure 3. 



Th<- figure beneath shows the same effect on the circle, and 

 nlwo gives tho i«iuare the apf.earance of being drawn in at the 

 middle of each side. Both these efforts arc shown much better 



with larger figures. All these diagrams form pregnant comments 

 on tho oft-repeated adage : " Cannot I believe my own eyes ? " — I 

 am, yours, Ac, Habbt Gbimshaw, F.C.S. 



Clayton, Manchester, Nov. 2Ut, 1881. 



CIRRUS CLOUDS. 



[112] — In reply to " Anti-Guebre " (letter 2. p. 15), scientific men 

 believe cirrus clouds to be composed of ice crystals because no 

 other reasonable explanation is available. These clouds are found 

 to produce certain optical effects upon light transmitted through 

 them which can only be explained by the theory of their crystaUine 

 nature, ice being tho only substance which will produce the 

 observed phenomena under tho conditions. This can be mathe- 

 matically proved. In conclusion, I would ask your correspondent, 

 Mr. G. F. P. Dyer (letter 20, p. 56), to refer to page 463-t of 

 Tyndall's " Heat," where it is stated that the aqueous vapour of 

 our air does absorb a very considerable amount of direct solar heat, 

 about four-tenths of the entire radiation ; these being chiefly dark 

 rays, which are the most effective as regards heating purposes. — 

 I remain, sir, yours truly, 



Birmingham. T. J. Hickin. 



VIVISECTION. INJURIES TO THE BRAIN. 



[113] — Most people think that of all cruel operations upon animals, 

 that of cutting the brain is beyond all the most cruel. The first 

 two extracts from recent numbers of the Laneet may modify their 

 opinion. The third extract is from " Body and Mind," by Henry 

 Maudsley, M.D., F.R.C.P., &c., &o. 



G. A., aged 15 years, met with an accident by which one-half of 

 the scalp was torn from the skull, which was itself fractured. From 

 between the edges of the broken bone, brain substance was oozing, 

 and this kept on for thirty-six hours. Recovery took place. The 

 points to be noticed are : — 



1. When the boy was found, he had already walked sixty yards 

 without any assistance from the place in the coal mine where his 

 head was crushed between a waggon and a rock, which forms the 

 side of the " waggon way," and he afterwards walked home. 



2. Although the injury was inflicted on March 6, 18St>, tho in- 

 tellect is not impaired or mind affected in any way. 



A man, aged 44, in an attempt at suicide, sent a small dagger 

 through his skull into the brain. He had held the dagger in his left 

 hand,l and given it with the right severnl blows with a mallet, be- 

 lieving that he would fall dead at tho first blow. To his profound 

 surprise he felt no pain. He struck the dagger in all about a dozen 

 times. When [seen, about two hours after, the handle was pro- 

 jecting, 9 centim^tre3 of the blade being sheathed in tho head. For 

 half-nn-hour unsuccessful attempts were made to pet the dagger 

 out with a strong pair of pincers, the patient being held firm on tho 

 ground by two vigorous persons. The patient, who walked well 

 and complained of no headache, was taken to a copjiersmith's, and 

 the dagger fixed to a chain passing over a cylinder turned by steam 

 power. The man was fastened to rings in the grotind. .A.t the 

 second turn of the cylinder the dagger came out ; the patient, who 

 had submitted to these mananivres, suffered no pain or incon- 

 venience. He walked to tho hospital, remained there for teB days 

 without fever or pain. He then returned to his work, and tho wound 

 healed. 



R. E. Wn-LUMS. 



[CundBiicJ on pane 181. 



