November io, 1921J 



NATURE 



JO' 



saw was a shadow moving on a screen ; what I heard 

 was a gramophone making nois<!S with all the familiar 

 defects. 



It is quite possible that in this case the synchronisa- 

 tion of film and record was not perfect, and that its in- 

 accuracy helped to destroy the illusion, but it must 

 be remembered that both one and the other — as Prof. 

 Rankine indicates in the case of speech records — 

 depend in great measure upon suggestion. The 

 dominant part of a word gives us the key to the 

 whole. Both words and pictures are scientifically 

 "imperfect," and when we attempt to amalgamate 

 them the resultant imperfection is so great that the 

 effect is wholly lost. Lough Pendred. 



33 Norfolk Street, Strand, London, W.C.2, 

 October 28. 



From practical experience I am able neither to con- 

 firm nor to contradict Mr. Pendred's interesting ob- 

 servations on the difficulty of practising simultaneous 

 deceptions on the senses of seeing and hearing. It is 

 quite possible, of course — perhaps likely — that it is 

 easier to produce one such effect than both at once ; 

 but I can see no reason, a priori, for expecting the 

 double deception to be impossible. It must be remem- 

 bered that both moving pictures and ordinarv gramo- 

 phones have been improved greatly during the years 

 since Mr. Pendred's experiences, and that, could 

 perfect synchronisation be guaranteed, the results he 

 describes might now be modified considerablv. Mr. 

 Pendred would. I think, admit that if both pictures 

 and sounds could be sufficiently improved, the remain- 

 ing imperfections, even though, possibly, additive, 

 might yet be so small that the decepticwis aimed at 

 would both be effective. 



There is no doubt that the photographic and photo- 

 electric method of recording and reproducing sounds 

 IS much superior to the comparatively coarse methods 

 used in ordinary- gramophones ; and this may 

 quite well be a reason, in addition to the attainment 

 of synchronisation, for the success of the talking 

 pictures produced by Mr. Bergland, and spoken of so 

 highly by the Times correspondent and bv Prof. 

 Arrhenius. A. O. Rankine. 



Royal College of Science. South Kensington, 

 London, S.W.7, November 2. 



The Differentiation of Boiled and Unboiled Water. 



It is often desirable to be able to ascertain whether 

 water alleged to have been boiled for drinking pur- 

 poses has in reality undergone the treatment. This 

 may be readily determined by means of indicators 

 appropriate to the type of water, for the effect of 

 boiling is always to lower the hydrogen-ion concen- 

 tration by removing carbon dioxide from solution and 

 decomposing bicarbonates. 



For example, Plymouth tap-water, a soft water 

 from Dartmoor, is now at /)H68, and gives a yel- 

 lowish colour with phenol-red. On boiling in a hard 

 glass test-tube it develops the full red with this 

 reagent, a light pink with phenolphthalein, and a 

 Yellowish colour with thvmol-blue. It is then at 

 JH8-5. 



"\oughal tap-supplv is at pHyo, but contains far 

 more bicarbonate than Dartmoor water, since on 

 boiling it not only gives the full red with phenol-red, 

 but also gives a more intense colour with phenol- 

 phthalein and a slaty-blue with thvmol-blue. denoting 

 ^Hqo, the limit for water saturated with calcium car- 

 bonate in absence of carbonic acid. 



\\'ater from Bla^don Reservoir (Bristol supplv) was 

 found to be at ^Hj-S, and at Pusa. in Bihar, the 

 laboratorv- taf>-water is at /)H8 i, that of the River 

 NO. 2715, VOL. 108] 



Gandak from which it is derived being somewhat more 

 alkaline. Running streams may be up to /)H8-3 even 

 when derived from wells at pHb-^. Saunders (Proc. 

 Cambr. Phil. Soc., 192 1, vol. 20, p. 350) has shown 

 that supplies in chalk and gault districts are at 

 pHji-y-2 very constantly, streams rising to 

 />H8-25-8-5. Sea-water is close to pHS-2. 



For these more alkaline waters phenol-red would 

 be an unsuitable reagent to detect the unboiled state, 

 as even in it the full red is developed, but phenol- 

 phthalein would ser\-e, showing either a colour or an 

 increase in intensitv with the boiled water. 



Higher limiting values may be obtained with waters 

 containing magnesium salts, since that for magnesium 

 carbonate, on boiling, is close to pHio-o. .Sea-water, 

 therefore, mav approximate to this, and fresh-water 

 from a small reser\-oir on Staddon Heights, Plymouth 

 Sound, was bv insolation with its naturally occurring 

 algae brought up to />Hq-7. 



On cooling, carbon dioxide is re-absorbed by boiled 

 water. This proceeds until the equilibrium with the 

 bicarbonate stage is reached, which is at />H8-37 for 

 saturated calcium bicarbonate. It is slightly lower 

 for water which has been boiled, since it can no 

 longer be saturated with respect to bicarbonate. This 

 stage still gives a f^ood colour with ohenol-red, being 

 more than /)H8. With water which is naturally at 

 this reaction when unboiled it is advisable to make 

 a direct test to ascertain the time that elapses before 

 the original reaction is regained, but a nositive result 

 mav alwavs be accepted as proof of boiling. 



Since onp omission to boil thf water may. especially 

 in the trooics. lend to a fatal illness, it is hoped that 

 the use of phenolphthalein. phenol-red. or other suit- 

 able indicator mav bp of use. W. R. G. Atkins. 



Marine Biological Laboratory-, Plymouth. 

 October "^i. 



Ophion iuteus. 



This flv. one of the larger Ichneumonidae, apf)ears 

 in mv house everv year in late summer. Several 

 members of my family have complained of being 

 stung by it, always at night, usually after they had 

 gone to bed in the top stor^-, third above the base- 

 ment. All doubt about the aggressor was dispelled 

 by a voung lady who, when reading in bed, felt a stab 

 on the arm and saw the insect flagrante delicto. 1 am 

 informed on high authority that, while Ophion is 

 one of the few Ichneumonidae which are known to 

 sting, and while a small, narrow^ poiscMi sac has been 

 detected in a few species of that immense family, none 

 has been recorded in Ophion Iuteus. But whereas 

 the sting is followed in even** instance by considerable 

 inflammation and pain, such as would not be the 

 effect of the mere stab of a needle, it seems almost 

 certain that some irritant is injected into the wound, 

 possibly for the purpose of paralysing the fly's legiti- 

 mate victim, as in the case of the hunting-wasps. 



It puzzles one to divine the purpose of Ophion in 

 attacking sleeping human beings. The weapon em- 

 ployed is the sharp point of the ovipositc»-. It seems 

 scarcely possible that the intention is that the progeny 

 should be lodged and fed in the body of man, .woman, 

 or child. What is normally the creature which 

 Ophion seeks as a harbour for its eggs and larx'ae? Is 

 this known ? Only once have I seen Ophion in my 

 own bedroom on the first floor. I was reading in 

 bed one night in August last when the fly alighted 

 on the sheet. I regret that instinct prevailed over 

 reason, and I destroyed the creature before the pur- 

 pose of its visit was revealed. 



Herbert Maxwell. 



Monreith, Whauphill, Wigtownshire, N.B. 



