46 



NATURE 



[September 9, 1920 



Letters to the Editor. 



[Tte Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected mantiscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



Relativity. 



The relativist position is stated as being " that only 

 relative motions are of physical importance." 



If this is meant to apply to rotation as well as to 

 motions of translation, and to deny that rotation is 

 absolute, and independent of the relation of the 

 revolving body to anything outside itself, I would 

 suggest that a relativist should try the following ex- 

 periment. Let two casks, A and B, of suitable sizes, 

 be placed one within the other (A inside), and so 

 mounted that either can be rotated independently. 

 Now let the believer in relativity place himself inside 

 A so that he can see nothing but its inner surface. 

 So far as appearances are concerned, he will not 

 know whether A is stationary or in motion. 



First let A be stationary and let B be made to 

 revolve at, say, looo revs, per minute. This will cause 

 no change of any sort in the sensations of the occu- 

 pant. Next, with B stationary, let A be given the 

 same angular velocity for a minute or two. If the 

 experimenter survives this trial, he will be in a posi- 

 tion to assert that the "physical importance" of the 

 angular velocity of A with reference to B is not tjje 

 same as that of B with reference to A. So far, how- 

 ever, as the geometrical relations of A and B are 

 concerned, it is a matter of indifference which of the 

 two is revolving. A. Mallock. 



9 Baring Crescent, Exeter. 



Toads and Red-hot Charcoal. 



Toads are associated with some wonderful myths, 

 and my scepticism was naturally great when my 

 friend Mr. H. Martin Leake assured me, while on 

 a visit to Cawnpore in October of 1915, that toads 

 would eat red-hot charcoal. .'\n after-dinner demon- 

 stration, however, soon dispelled my doubts. Small 

 fragments of charcoal heated to a glowing red were 

 thrown on the cement floor in front of several of the 

 small toads (usually Bufo stomaticus) which so com- 

 monly invade bungalows at that time of year, and, to 

 my surprise, the glowing fragments were eagerly 

 snapped up and swallowed. The toads appeared to 

 suffer no inconvenience, since not only did they not 

 exhibit any signs of discomfort, but, on the contrary, 

 several toads swallowed two or even three fragments 

 in succession. A probable explanation of the picking- 

 up is that the toads mistook the luminous pieces of 

 charcoal for glow-worms or fireflies, the latter being 

 numerous in the grounds of the Agricultural College 

 at Cawnpore in October ; but this does not account for 

 the swallowing of the hot partfcles — the absence of 

 any attempt to disgorge. I repeated the experiment at 

 Allahabad in August, 1916, with the same results (the 

 toads even attempting to pick up glowing cigarette- 

 ends), though I have never observed glow-worms or 

 fireflies in Allahabad at any time of year. 



The fact that some toads seized several hot particles 

 in succession would seem to imply either that the heat 

 was not felt (which seems incredible), or that memory 

 is entirely absent in toads ; but since toads most cer- 

 tainly come to associate a given time of day with the 



NO. 2654, VOL. 106] 



supply of food, i.e. remember, this latter explanation 

 seems to be equally incredible. The truth must be 

 that the incentive to seize an object (a luminous point 

 in this instance) usually associated with an insect is 

 so strong that even acute pain is no deterrent when 

 the experience is limited — the lessons of experience 

 out of the ordinary require to be " burned " into the 

 toad intelligence by sheer repetition, just as the im- 

 prisoned shark which repeatedly bruises its snout 

 against the glass of its tank has the lesson 

 " knocked " into it in time. I may add that I unfor- 

 tunately neglected to exsunine the toads post-mortem, 

 and that I have recently rejjeated these expyeriments 

 with Bufo vulgaris in England with entirely negative 

 results. W. N. F. Woodla.vd. 



" Kismet," Lock Mead, Maidenhead. 



Active Hydrogen. 



In March last 1 observed an interesting pheno- 

 menon while conducting certain experiments, in the 

 Maharajah's College, Vizianagaram, with detonating 

 mixtures with excess of hydrogen when they are sub- 

 jected to the silent electric discharge in an ozoniser. 

 In one experiment the oxy-hydrogen mixture, after 

 leaving the ozoniser, was allowed to pass through an 

 alkaline solution of potassium permanganate. In the 

 course of the experiment an electric spark accidentally 

 took place in the mixture, and as a consequence an 

 explosion occurred in which a part of my apparatus 

 was smashed to pieces ; but to my surprise I found 

 that the whole of my permanganate solution turned 

 green at once. 



It was surmised from this that the instantaneous 

 reduction might be due to the presence of an active 

 modification of hydrogen produced in the circum- 

 stances, since molecular hydrogen brings about the 

 same change very slowly. In order to study the 

 problem more conveniently, I filled a Hofmann 

 eudiometer with an alkaline solution of potassium 

 permanganate, and a few cubic centimetres of 

 an explosive mixture w-ith excess of hydrogen 

 (3 vols, of hydrogen and i vol. of oxygen) were ad- 

 mitted into the explosion tube and the mixture was 

 sparked ; as soon as the spark passed through the 

 solution it turned green. 



With the object of testing further the reducing 

 efficiency of this new form of activated hydrogen, its 

 effect was examined in a number of reactions. It 

 was thus found that with this hydrogen an alkaline 

 solution of indigo was converted into indigo white, 

 ferric chloride into ferrous chloride, potassium nitrate 

 into potassium nitrite, arsenious acid into arsine, 

 potassium perchlorate into potassium chloride, and a 

 number of ether reactions were also tried with like 

 results. 



Some references to the literature relating to this 

 subject of active hydrogen may be of interest. In 

 1913 Sir J. J. Thomson was led to conclude from 

 examination of the paths of positively charged par- 

 ticles that they "revealed the presence of particles 

 having an atomic weight of 3, presumably triatomic 

 molecules of hvdrogen." Duane and Wendt showed, 

 in 1Q17, that when hydrogen is exposed to the bom- 

 bardment of a-particles from radium emanation a 

 contraction in volume occurs, a fact which has 

 been incidentally observed by Usher, and con- 

 firmed recently by Lind. In 1912 Dr. Langmuir 

 discovered an active modification of hydrogen by 

 heating a metallic filament in hydrogen at low pres- 

 sures. .Again, so late as May last, Gerald and Robert 

 S. Landauer published a paper on triatomic hvdrogen 

 in the Journal of the .American Chemical Society. 



