to 
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No 
NATURE 
[ JANUARY 7, 1904 
after the death of the former, whose soul is transported 
to Mars, they get into communication with each other. 
The posthumous papers consist of the record left 
by the son, who describes all their experiments, hopes, 
failures, successes, and, lastly, the extra-planetary 
wireless messages he received. 
Those interested in this class of fiction can spend 
a pleasant hour or two over these pages. 
On the Lakes of South-eastern Wisconsin. By Prof. 
N. M. Fenneman. Bulletin viii. of Wisconsin Geol. 
and Nat. History Survey. Pp. xv+17 (Madison, 
Wisconsin : Published by the State, 1902.) 
Tue preface and the introduction announce the object 
of this work. It is intended as a guide to the teacher 
of geology, and shows how the shores of these lakes 
may form beautiful illustrations of the principles of 
wave, current, and ice action. The first chapter gives 
a general account of the origin of such lakes, and the 
second is devoted to a general and more or less theo- 
retical discussion of the geological agents at work. 
After this the lakes are taken up one by one, and it is 
shown how the various features of the shore have 
arisen. There are many very good and aptly chosen 
photographs, which bring out clearly the points 
mentioned in the text, and make the book interesting 
even to those who cannot see the lakes for themselves. 
Most of the book is devoted to the features of the 
shores, but it is also shown how the hydrographic 
maps may be used to decipher the origin of the basins, 
and in the case of Lake Mendota there is an interest- 
ing discussion of the results obtained by dredging, 
which are said to indicate currents below the wave- 
base. The unpublished worl of the director of the 
Survey, Dr. Birge, on the temperature of these lakes 
is also said to confirm these conclusions. We shall 
look forward to the publication of these temperature 
observations. IDey 1 MWY 
Malessere Agrario ed Alimentare in Italia. By Italo 
Giglioli, Direttore della R. Stazione Agraria di 
Roma, &c. Pp. Ixxxii+797. (Portici, 1903.) 
In this work Prof. Giglioli has attempted a detailed 
survey of the agricultural state of Italy in comparison 
with other nations. He considers one by one the 
various branches of the industry, the production of 
wheat, maize, rice and other cereals, wine, fruit, olives 
and silk, eggs, butter, cheese and the many minor 
branches of rural activity which are possible in the 
climate of Italy. In each case a comparison is drawn 
between the conditions of the past and those which 
prevail to-day both in Italy and the chief competing 
countries. Both as an ardent patriot and a man of 
science, Prof. Giglioli is troubled by the increasing 
poverty of the rural districts as compared with the 
towns, especially when one travels out of the favoured 
northern provinces of Lombardy and Tuscany into 
middle and southern Italy. He indicates how the 
actual production of the land is declining, so that Italy 
with all its traditional farming skill and with the vast 
possibilities of its climate is coming to be more and 
more dependent upon other nations for food which 
could be grown within its own borders if only more 
intensive methods of cultivation were resorted to. 
Aggravated as the case is in parts of Italy by the 
poverty of the people and their entire dependence upon 
agriculture, the problem is one which all the west 
European States are being called upon to face; how 
can agriculture, which is a primitive industry, live in 
a highly civilised State against the competition of the 
great areas of virgin soil like Argentina or the North- 
West? To English economists who want an en- 
lightened and temperate review of the situation in a 
macnn not unlike our own we commend Prof. Giglioli’s 
book. 
NO. 1784, VOL. 69] 
LETTERS TO THE EDITOR. 
(The Editor does not hold himself responsible for opinions 
expressed by his correspondents. Neither can he undertake 
lo 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.] 
Does the Radio-activity of Radium depend upon its 
Concentration ? 
Some experiments have recently been made to test whether 
the radio-activity of radium is influenced by the continuous 
bombardment to which it is subjected by its own radiations. 
In an article in this Journal on radium (April 30, 1903) Prof. 
J. J. Thomson suggested that the radio-activity of radium 
may possibly depend upon its degree of concentration, and 
that a given quantity of radium, diffused throughout a mass 
of pitchblende, may be less than when concentrated in a 
small mass. In order to test this point, measurements of 
the radio-activity of radium bromide were made when in 
the solid state and when diffused throughout the mass of a 
solution more than a thousand times the volume occupied 
by the radium compound. 
Two tubes, closed at one end, were taken, in one of which 
was placed about a milligram of pure solid radium bromide 
and in the other a solution of radium chloride. The tubes 
were connected near the top by a cross tube, and the open 
ends were then sealed by a blowpipe. 
Measurements of the radio-activity of the radium were 
made by means of an electroscope. The tubes, fixed on a 
stand, were placed in a definite position near an electroscope 
and the rate of discharge observed. This was due to the 
B and y rays emitted by the radium, since the a rays were 
completely absorbed in the walls of the tube. By placing 
a lead screen 6 mm. thick between the tubes and the electro 
scope the rate of discharge was due to the + rays alone. 
After measurements of the activity had been made, the 
glass apparatus was tilted so as to allow the radium chloride 
to flow into the arm containing the radium bromide. This 
dissolved the radium, and part of the emanation was re- 
leased and distributed itself throughout the tubes. 
No appreciable change of the radio-activity of radium was 
observed over a month’s interval. If the rate of pro- 
duction of the emanation, or the excited activity taused by 
it, had varied during the interval, a corresponding change { 
would have been observed in the rate of discharge due to 
the y rays, for other experiments have shown that the 
amount of y rays is proportional to the amount of eman- 
ation present, provided measurements are made several 
hours after the introduction of the emanation into a vessel, 
in order to allow the excited activity to reach a maximum 
value. The rate of discharge due to the y rays was some- 
what diminished, but this was due to an increased absorp- 
tion of the B rays by the solution, and not to a change in 
the rate of emission of these rays. On account of the great 
penetrating power of the y rays, the increased absorption 
due to the presence of the solution was negligible. 
Since, after solution, the radium bromide was diffused 
through a mass of solution at least 1000 times the bulk of the 
solid radium bromide, we may conclude that a distribution 
of the radiating matter over a thousand times its original 
volume has no appreciable influence on its radio-activity. 
This experiment shows that, over the range investigated, 
einen 
the radio-activity of radium is not influenced by its own — 
intense radiations. This result is in agreement with previous — 
observations, for neither the radio-activity of any active pro-— 
duct nor the rate of loss of its activity has been found to ~ 
be affected by its degree of concentration. 
It is thus improbable that the energy given out by radium 
is due to an absorption of an unknown external radiation 
which is similar in character to the radiations which are © 
emitted. Experiments are in progress to test whether still 
further dilution of the radium solution produces any alter- 
ation in its radio-activity. E. RUTHERFORD. 
McGill University, Montreal, December 18, 1903. 
Relative Motion and Conservation of Energy. 
I nAVE received a letter from a correspondent which has 
led me to think that certain points connected with elemen- 
tary dynamics are very obscurely put forward in text-books 
and in elementary class teaching generally. Of these the 
following may be taken as examples :— 
rr. 
