460 



NA TURE 



[June 16, 1910 



glance at my letter again, he will see that, speaking of 

 the various forms which I had used or had under con- 

 sideration during the preceding five years, I said that in 

 that year (1874) " the form raiian was definitely adopted 

 by me." It is the words jorm and fcy me that here make 

 all the difference. 



The same mail steamer which brought Mr. Thomson's 

 letter brought for delivery a few hours later a tattered 

 copy of the third edition of Todhunter's " Plane Trigono- 

 metry," sent to me as evidence of a still earlier use of 

 the word " radial " to denote the unit-angle in question. 

 This text-book was the property of a pupil of mine in 1867, 

 and it contains in my handwriting of that date the words 

 '■I radial = i8o°/7r, i degree = 7r/i8o rad." When next in 

 England I shall offer it for your own and Mr. Thomson's 

 inspection. Thos. MuiR. 



Cape Town, South Africa, May 11. 



I SHALL be very pleased to send Dr. Muir a copy of my 

 father's examination questions of June, 1873, containing 

 the word radian ; and when Dr. Muir returns to England 

 I should like to show him my father's copy of the 

 " Imperial Dictionary " containing a note in his own 

 hand saying that he had proposed the word in July, 1871. 

 So tar as I know, he did not meet Dr. Muir until he came 

 to Glasgow in October, 1873. 



It thus appears that radian was thought of independently 

 by Dr. Muir and my father, and, what is really more 

 important than the exact form of the name, they both 

 independently thought of the necessity of giving a name 

 to the unit-angle. James Thomson. 



22 Wentworth Place, Newcastle-on-Tyne, June i. 



The Nutritive Value of Black Bread. 



In the issue of Nature for June 2 (p. 398) there is a letter 

 from a correspondent in reply to the article on " The 

 Nutritive Value of Black Bread." The correspondent 

 points out that the writer of the article overlooked one 

 all-important question, viz. how much of the nitrogen 

 present in each form of bread is actually digested? In 

 the original article the writer complained that misleading 

 statements were made by some politicians during the last 

 Parliamentary General Election with regard to German 

 black bread. No doubt some of your readers expected to 

 see a letter or two in reply to this complaint. There has 

 not been one. 



Now what are the facts with regard to German black 

 bread? What the people of the United Kingdom care 

 about is what their bread will cost. They do not care 

 whether that bread, which the Germans themselves call 

 " black bread," is black, or brown, or grey. The follow- 

 ing are the prices obtained from a large bakery in the 

 town of Elberfeld last December :— 



Flour. 

 Description 



Finest wheat flour 

 Wheat flour 

 Best rye flour ... 

 Ammunition flour 

 Coarse rj-e flour 



Pi ice I'er 

 14 lbs. 



54 



9^ 



Bread. 



Price per 

 Descrip ion 4 lb. loaf 



d. 

 White bread, made with milk and wheat flour 9! 

 Fine bread, made of wheat and water ... ... 8j 



Rye bread, pure 6 



Rye + wheat (J wheat -t-f rye) 6 



Rye-i- wheat (| wheat + f rye) 6 



Ammunition bread 5! 



Black bread ... ... ... ... ... ... 5 



From the above figures, which have never been challenged, 

 your readers can draw their own conclusions. 



Protectionists are most anxious to prove that rye bread 

 is good, and they suggest that it is preferred to wheat 

 bread. Free Traders never denied that rye bread was 

 good. They stated that it was an inferior bread to wheat, 



and that the chief reason for its use in Germany was its 

 lower price in comparison with wheat bread. Rye costs 

 less than wheat in Germany, and this is a proof that it 

 is an inferior grain. The bread which is reckoned the 

 finest bread is wheat bread, all the world over, and in tht- 

 best hotels in Germany it is regularly served with all 

 meals. On account of the duty the price of wheat bread 

 is too high in Germany for working-class people, and they 

 buy breads made from mixtures of cheaper grains, accord- 

 ing to price. The " black bread " in Elberfeld is made 

 from a Verj^ coarsely ground rye flour, and it is sold and 

 spoken of as "black bread," although it is a very dark 

 brown in colour. Fred Smith. 



92 Halsbury Road, Fairfield, Liverpool, June 4. 



It is assumed in the letter that the whole difference in 

 price is due to the duty on wheat. But an examination 01 

 the figures given shows that the cost of the various bread- 

 is not closely proportionate to the price of the flours, and 

 it would seem that the bakers take a much larger profit 

 on the wheaten bread. Indeed, this must certainly be so 

 unless the yield in bread from a given weight of rye flour 

 is much larger than from a similar weight of wheaten 

 flour, a point upon which no information is to hand. 



The Writer of the Article. 



The Recoil of Radium B from Radium A. 



When radium A is transformed into radium B, thf 

 process is accompanied by the expulsion of an o particle. 

 It has been shown that in these circumstances the atom 

 of radium B recoils from the o particle with considerable 

 velocity, as is to be expected from a consideration of the 

 momentum of the system. 



Some experiments have recently been made to determine 

 whether radium B is charged when it recoils, and, if so, 

 to ascertain the sign of the charge carried by it. Measure- 

 ments to determine whether the radium B was deflected 

 when passing through an electrostatic field revealed the 

 fact that at least some of the atoms of this product, on 

 formation from radium A, carried with them a positive 

 charge when projected through a high vacuum. Experi- 

 ments were therefore made to measure the magnitude of 

 the deflection suffered by the atoms of radium B whert 

 projected through an electric field at right angles to the 

 direction of motion of the particles. 



Now, since the o particles from radium A travel with 

 a velocity of 1-77x10' centimetres per second, the recoil- 

 ing atoms of radium B should 'nave a velocity of 3-3x10^ 

 centimetres per second, on the assumption that the atomic 

 weight of radium B is 214 and that of the o particle 4. 

 The deflection to be expected when subjecting the recoil 

 particles to a field of known strength can easily be calcu- 

 lated if it be assumed that each particle carries one atomic 

 charge, or half that carried b}' an o particle. The results 

 of the experiments to deflect the radium B in an electro- 

 static field were consistent with this theory of the pheno- 

 mena, but the experimental difficulties were such as to 

 prevent us, so far, from making very accurate determina- 

 tions. 



Before attempting to make these measurements with 

 greater accuracy, it was thought of interest to investigate 

 the deflection of radium B in a magnetic field. This has 

 been done by Mr. E. J. Evans and one of us, and tli 

 results obtained show that when radium B recoils throu| 

 a magnetic field the deflection suffered by the particles 

 of the size to be expected from theory. 



Taken together, the results of the electrostatic and mafi 

 netic deflections of the atoms of radium B after recc 

 leave little doubt that the atomic weight of radium B 

 in the neighbourhood of 200, that this product carries wi 

 it on recoil a single positive atomic charge, and that th 

 velocit)' of the particles is of the order of magnitude t^ 

 be expected from considerations of momentum. It 

 however, hoped that subsequent experiments may lead 

 a determination of these important quantities wit 

 accuracy. W. Makower. 



S. Russ. 



Physical Laboratory, The University, 

 Manchester, June 10. 



NO. 2120, VOL. 83] 



