126 
NATURE 
| DecEMBER 6, 1906 
the progress of natural history in this country and the 
evolution of the collections in the Museum which it 
would be very difficult, or impossible, to obtain else- 
where. Despite a lamentable loss of early collections, 
like those formed during Cook’s voyages, owing to 
lack of knowledge of their value and_ indifferent 
curatorship, the Museum is particularly rich in type- 
specimens, more especially of species presenting well- 
marked characteristics of their own. In many cases 
particular attention is directed to these and other 
specially interesting specimens in the collection, 
although in these matters, again, a great diversity of 
treatment is noticeable in the different accounts. 
By the Rev. Lord William 
Gascoyne Cecil. Pp. 105. (London: Hodder and 
Stoughton, 1906.) Price 3s. 6d. net. 
Five addresses delivered in substance at St. Lawrance 
Jewry during Lent, together with an explanatory 
foreword, make up the contents of this volume. The 
author lays claim to ‘‘no scientific qualifications at 
all,” and therefore ‘“‘can only speak as one of the 
crowd,’’ to use his own description of himself. The 
sermons follow lines which are already familiar to 
students of science acquainted with the literature 
which has grown up round the attempt to ‘ reconcile ’’ 
traditional theology with results of scientific study. 
Science and Religion. 
How to Learn on Shore the Rule of the Road at Sea. 
By E. W. Owens. Pp. 40+23. (London: George 
Philip and Son, Ltd., 1g06.) Price 3s. 6d. net. 
Tuis excellent little book meets a great want, and is 
strongly recommended for use in all training schools 
and ships. It is arranged in a convenient manner, 
and the explanations are simple and good. Part ii., 
which consists of extracts from the Merchant Shipping 
Act and the latest regulations for preventing 
collisions at sea, special lights for fishing craft, &c., 
makes the book not only useful in the class-room, but 
a great convenience on the bridge of any ship as an 
aide mémoire. H. C. Lockyer. 
LETTERS TO THE EDITOR. 
(The 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 
manuscripts intended for this or any other part of NaTuRE. 
No notice is taken of anonymous communications. ] 
Absorption of the Inert Gases by Charcoal. 
Iv may interest some of your readers to know that Prof. 
Rutherford, in a private letter addressed to myself, has 
given a full explanation of the circumstances that led him 
to infer that the absorption of the inert gases by char- 
coal was exceptional. Fully appreciating the difficulties 
that beset Prof. Rutherford at the time he wrote the letter 
to Nature (vol. Ixxiv., p. 634, October 25), I exonerate 
him from all blame in the matter, and willingly cancel all 
the expressions of regret he has been pleased to make. 
With regard to the latent heat question, I ought to 
mention that Prof. Rutherford will not commit himself 
to the view that the electrometer readings recorded in 
the paper I quoted are proportional to the partial pres- 
sures of the emanation. He says:—‘‘I do not know how 
far the electrometer readings may be taken as a measure 
of the partial pressures of the emanation, but naturally 
measurements over a range of temperature of 1° or 2° 
cannot be vouched for with any certainty.’ This would 
be a strong criticism provided any manometric measure- 
ments had been attempted, but if the electrometer measures 
directly the relative concentration of the emanation in a 
given volume of gas, the method is so sensitive that the 
merease caused by a narrow range of temperature is less 
liable to error. It is clear, however, that new determin- 
ations will have to be made before the question can be 
settled. 
NOw 1936; VOL. (75) 
i 
' 
In the meantime, I can only wish Prof. Rutherford 
success in the applications of charcoal to the study of the 
emanations of radio-active bodies, and take the oppor- 
tunity of expressing my gratification at seeing charcoal 
becoming of such scientific utility in the hands of workers 
like the Hon. R. J. Strutt, the French chemists Moureu 
and Biquard, not to mention others: the more especially 
as my own labours have been interrupted for reasons 
given in my former communications 
James Dewar. 
Royal Institution, 21 Albemarle Street. 
Radium, Actinium, and Helium, 
Ix Nature of November 29 Dr. B. Walter discusses the 
theory of Prof. Rutherford that in radio-active change 
accompanied by the emission of an a particle the atomic 
weight is diminished by 4, the atomic weight of helium. 
According to this assumption, the transformation of 
uranium (238-5) into radium (225) is due to the loss of 
three helium atoms. Now uranium gives one a particle 
in changing to uranium X, so that only two such changes 
remain for any subsequent transformations. If we accept 
the result of Profs. Moore and Schuldt (Phil. Mag., 
October) that uranium X gives out a rays, two changes are 
accounted for, and only one is left for intermediate pro- 
ducts. 
In Nature of November 15 Mr. Boltwood brings for- 
ward experimental evidence in support of the view that 
actinium is an intermediate product between uranium and 
radium; but in the case of actinium and its derivatives 
four changes, accompanied by the emission of a particles, 
occur. Thus, on the assumption that the a particle is a 
helium atom, there is no room for these products. 
The difficulty can be removed by adopting another 
alternative, suggested by Prof. Rutherford, that the 
a particle is one-half of the helium atom carrying a single 
ionic charge (Phil. Mag., p. 366, October). In this case 
we should have the following series possible :— 
Serzes I. | Serves Lf. 
Uranium (238°5)—a [ae (235°5 —a 
Uranium X (236°5)—a, B, 7 | Uranium X (236'5)—a, B, 
| 
| Unknown (234°5)—a 
| 
| selieunm (232°5) 
Actinium (234°5) 
Radio-actinium (234°5)—e 
Actinium X (232°5)—a | Radio-actinium (232°5)—a@ 
Actinium emanation (230°5)—a Actinium X (230°5)—a 
Actinium A (22S 5) Actinium emanation (228°5)—a 
aewa| 
| 
Actinium B (228'5)—a, 8, 7 | Actinium. A (226°5) 
Unknown (226°5)—a Actinium B (226°s)—a, B, y 
| 
Radium (224°5) | Radium (224°5) 
If the atomic weight of radium were 226-5, the unknown 
change accompanied by the expulsion of an a particle 
must be removed from the series. One or more rayless 
changes may also occur. 
It is interesting to note that the atomic weight of 
actinium, according to Series II., comes out as 232-5, that 
is, exactly the atomic weight of thorium. These two sub- 
stances closely resemble one another in their radio-active 
properties, giving transformation products of very similar 
character. This suggests as an analogous case the 
similarity between nickel and cobalt, two elements of prac- 
tically the same atomic weight. H. S. ALLEN. 
King's College, London, November 30. 
Mira Ceti. 
Ir may be well to note that this variable star is ex- 
ceptionally bright at its present maximum, the magnitude 
being about 2-0. As usual when the star is bright, it is less 
red than its average. T. W. BackHOUSE. 
West Hendon House, Sunderland, December 1. 
