312 



NA 7 URE 



July 31, i! 



trical resistance, the number of B.A. units adopted as represent- 

 ing the resistance of a column of mercury loo centimetres in 

 length, one square millimetre in section, at a temperature of 

 o° £. be '9540." 



Il follows from this that the legal ohm of the Paris Con- 

 gress, which is define. 1 as the resistance of such a column 106 

 cm. in length, contains 10112 B.A.U., while the B.A.U. 

 contains -0889 legal ohm. Thus resistances which are expressed 

 in terms of B.A. units may he reduced to legal ohms by multi- 

 plying by -9889, while makers and others who have a standard 

 B.A. unit can construct a legal ohm by making a coil equal to 

 1 'oi 12 times that unit. 



A 1 solution of the nature of the above was rendered neces- 

 sary by the fact that the legal ohm is defined in terms of the 

 resi eof a column of mercury, while the resistances in use 



in England are B.A. units. The relation between the two has 

 been determined by different observers with slightly different 

 results. The Committee hope to secure uniformity in the re- 

 sold to the public as legal ohms, by stating the number 

 they intend to adopt for the purpose of issuing standards. 

 R. T. Glazebrook, 

 Secretary Electrical Standards Committee 

 of the British Association 



The Yard, the Metre, and the Old French Foot 

 The ratio of the metre to the yard can scarcely be said to be 

 known with certainty at the present day. The latest and most 

 exhaustive investigation of this question is due to Prof. W. A. 

 Rogers of Cambridge, Mass. The value which he assigns to it 

 (pending a final and authoritative comparison of the "Metre des 

 Archives " with its chief representative, by the International 

 Commission of Weights and Measures) is — 

 3937027 : 36. 

 This ratio is very nearly identical with the much simpler one— 

 35 t 32. 

 the error of which is less than I in Socio. If we disregard this 

 error, the conversion of yards into metres can be effected with the 

 greatest ease by the following arithmetical process. Thus — 



Given 35 yards or 39'37°27 yards 



.subtract i/ioth - 3'5 ~ 3'937°27 



Add i/7th + -5 + -5624324 



Results 32-0 metres 35-9956754 metres 



Error - -0043246 

 By a singular piece of good luck, this error, small as it is, maybe 

 entirely removed by one more easy approximation : for dividing 

 the last quotient by 1 30 gives + -0043263— where the out- 

 standing disagreement is less than a unit in the last given figure. 

 Hence, if we wish for a closer conversion than will be given by 

 the terms 1, - iV, + i (of the last), we have only to add further, 

 + T j iTi (of the last) to obtain the utmost accuracy at present 

 possible. 



The converse operation — to convert metres into yards — is not 

 quite so short and easy in the closer approximation. The follow- 

 ing shows the approximate and the more exact conversion : — 



Given 



Add i/ioth ... 



Subtract 11 6th 

 ,, 2/iooths 

 ,, l/20th .. 



32 metres 36 metres 

 3-2 + 3'6 



- 0-225 



- '0045 



- -000225 



0'2 



Results 35-0 yards 39-370275 yards 

 The fact is. almost any conversion may be performed in some 

 such way, in three or four operations; and it was not for the 

 sake of the rigorous ones that this note was written, so much as 

 n, bring into notice the very close and useful approximation 

 represented by the ratio 32 : 35. 



By way of applying the rules usefully, we may take as 

 ':— To find the equivalent of a kilometre in yards, and 

 of a mile in metres. Thus — 



6-25 



•125 ... . 

 00625 



Answers 1093-61875 yards 



1760 yards 

 - 176 



+ 25-14286 

 + 'I934I 



1609-3363 metres 



Here we see that the approximate ratio 32 : 35 entails an error 

 of only 0-131 yard (or less than 5 inches) in one kilometre ; or of 

 0-193 ( or Iess tnan 2) decim. in one mile, so converted. 



The old French foot, the sixth part of the toise — the famous 

 "Toise of Peru " — survives now practically only in the Prussian 

 toise, so far as that is not superseded by the metre. Whatever 

 may be its present range, the ratio of the old French foot to the 

 present English foot is curious. I believe it may be expressed, 

 within the limits of error of the relation so far as can now be 

 known, by the fraction 389/365. That is to say, the excess of 

 the former is 24/365 x the latter, the two components of which 

 fraction are such as may easily be remembered when once the 

 coincidence has been noted. J. Herschel 



Collingwood, July 25 



Fireballs 

 In reference to the phenomena of fireballs the following notes 

 may be of interest. Last year, in July, I was residing on 

 Naphill Common, Buckinghamshire. About midday, during my 

 absence at Oxford, a violent thunderstorm broke over the 

 district, and appeared to extend from Oxford to London. On 

 returning I found that the house had been struck by lightning, 

 apparently in two places. One chimney was knocked in 

 through the roof, the debris partly filling up my room. The 

 kitchen chimney had also been visited, the lightning breaking 

 some of the brickwork of the hearth, and passing a person 

 cooking at the fire ; two or three others were in the house 

 at the time, but no one was hurt. On carefully examining 

 the marks left, I found that a door in a room adjoining the one 

 above-mentioned had been split, and some iron knobs knocked 

 off and broken, the screw nails being removed out of the wood, and 

 a large hole several feet square made in the side of the house. From 

 examination of the outside of the wall at the foot of the kitchen chim- 

 ney, the bricks showed displacement opposite the marks inside at 

 the hearth. I believe a tree was struck, and a water-trap or cess- 

 pool shifted out of position. Some men using a reaping machine 

 in a neighbouring field stated that they knew the storm was 

 coming by the fire playing about the blades of the machine. A 

 boy who had been near at the time said that he saw a large ball 

 of fire fall on the house, which it seemed to enter ; it then re- 

 appeared, and passed into the meadow. I therefore think it 

 likely that the damage done to the rooms and side of house was 

 due to the electric development called a fireball. 



Glasgow W. J. Millar 



Tne Swallowing of one Snake by another 

 As the author of the article " A Cannibal Snake " (Nature, 

 July 3, p. 216) wishes to know whether an instance similar to 

 that recorded by him has ever before been brought to notice, I 

 feel bound to publish an occurrence which I witnessed many 

 years ago, and of which I have often told, without ever putting 

 it into writing. During the summer of 1857 I lived in the 

 environs of Washington ; as an amusement, snakes were kept in 

 cages. Sometimes, in the evening twilight, when toads and 

 frogs appeared on the garden paths we used to feed the snakes 

 with them. The usual habit of the snakes was to seize the toad 

 wherever the jaws happened to strike, and to move them after- 

 wards along the body of the victim, so as to begin the process 

 of swallowing from the head. Once I threw a toad into a cage 

 containing two of the common water-snakes of that region 

 (Nerodia sipedon, if I recollect right, is the scientific name of the 

 species). Both seized the toad at the same time ; the one near 

 the head began at once to swallow ; the other put its jaws in 

 motion as usual, in order to get at the head, but in doing this it 

 reached the head of its comrade, and began to swallow that, as 

 well «t the toad. This went on for some time, until about 

 three-quarters of the one snake were ingulfed within the other. 

 Then the snakes separated again, the swallowed one coming out 

 covered with slime, but apparently unhurt and as lively as ever. 

 It lived a long time afterwards. The snakes were of about 

 equal size, and, as far as I remember, from 2i to 3 feet long. I 

 suppose that it was the swallowing snake, and not the swallowed 

 one, that kept the frog, but I do not think I ascertained the fact 

 at the time. The whole performance lasted a few minutes only. 

 Heidelberg, Germany, July 27 C. R. Ostf.n Sacken 



The Red Sunset3 



I NOTE in Nature of July 3 (p. 229) an abstract of a com- 

 munication of M. Gay to the Paris Academy of Sciences, made 



