JULY 1, 1915] 
are added after all measurements in metres or 
in centigrade degrees. Besides the translator’s 
interpolations, an unnamed editor has inserted in 
the text many notes which would have appeared 
more appropriately at the foot of the page. As 
these notes are on astronomical points only, they 
leave the impression that other subjects stand in 
similar need of amendment, and there can be no 
doubt that this is the case in more than one 
chapter. 
Sometimes the author writes with a little too 
much confidence. He treats a theory almost as 
if it were a scientific fact. For instance, he 
refers to the contraction theory of mountain- 
formation as though its foundation were secure. 
He accepts as proven an eleven-year period of 
earthquake-frequency and the increased frequency 
of earthquakes at the times of the equinoxes. 
While reading the book, it is difficult to resist 
the impression that the author does not always 
trust to original authorities. This impression is 
perhaps strongest in the chapter on seismic phe- 
nomena, in which, though the original text must 
have been written in or after 1909 (see p. 208), 
many facts are omitted which should have found 
a place. Indeed, in this chapter of thirty-eight 
pages, the name and work of Milne are never once 
mentioned. 
A Map of the Western War Area. Edited by 
> Protageaeme)|. etlerbertsonsammoom un. x60) in: 
(Oxford: The Clarendon Press.) Price, mounted 
in sections, with names 15s., without names 
12s. 6d. 
Tus useful and striking map depicts the country 
from the Seine to the Rhine, and from the Swiss 
frontier to the Rhine delta, on a scale of eight 
miles to 1 in. (1: 500,000). It is provided with 
contour lines and layered colouring, and shows 
vividly the interdependence of land relief and 
military strategy. It is issued in several forms— 
unmounted, mounted in sections, and mounted 
on rollers, varnished or unvarnished, at prices 
varying from tos. 6d. to 17s. 6d. Produced under 
the supervision of Prof. Herbertson, it provides 
an excellent and trustworthy companion for the 
student of current events in France. 

CERT ERS TO REESE DITOR. 
{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. | 
A Canadian Memorial to Hugh Miller. 
In a letter which I have just received from Dr. 
John M. Clarke, director of the State Museum at 
Albany, N.Y., he writes :—‘* You may be interested 
to know that at my urgent suggestion the Geographic 
Board of the Province of Quebec have adopted the 
name ‘Hugh Miller Cliffs’ for the wonderful Old 
Red Sandstone fish-beds which line Scaumenac Bay 
on the Bay Chaleur, near the Gulf of St. Lawrence. 
I think there is no place in the world where the fishes 
Hugh Miller described are so abundant. It is a little 
NO. 2383, VOL. 95] 
NATURE 
479 

odd that the devout French Catholics of P. Quebec 
should consent to this naming of their scenery after 
a Scotch Presbyterian, but the cliffs look across the 
bay from French Quebec to Scotch New Brunswick !”’ 
Geologists in this country will be pleased to hear 
of this Transatlantic recognition of Miller’s pioneer 
work, and they will feel that Dr. Clarke, who is 
amiliar with the classic Cromarty ground, as well as 
with that of Scaumenaec Bay, deserves our thanks for 
suggesting this unusual but most appropriate memo- 
rial, and for his successful efforts to have it carried 
our. ARCH, GEIKIE. 
Shepherds’ Down, Haslemere, June 24. 
The ‘‘ Green Fluorescence’ of X-Ray Tubes. 
Tue Glass Research Committee of the Institute of 
Chemistry has recently issued a note on_ the 
conditions for obtaining green fluorescence under 
kathode rays in glass suitable for X-ray tubes indi- 
cating that the presence of a small amount of man- 
ganese must be present. In view of the fact that 
there appears to be some misconception regarding 
the necessity of the green fluorescence it may be of 
interest to give a brief account of what is involved in 
obtaining as marked a fluorescence as that which 
has usually been noticed in working X-ray tubes 
hitherto. 
So far as I am aware the advantage of the green 
fluorescence is that it provides the X-ray operator 
with a convenient rough indication of the ** hardness” 
of the tube. It is scarcely necessary to point out that 
the quality of the X-rays is in no way influenced by 
the nature of the fluorescence of the glass. Experi- 
ment has shown that a strong green fluorescence can 
only be obtained at some sacrifice of the excellence 
of the glass. Glass manufacturers frequently add 
manganese dioxide to a glass mixture to correct the 
green colour due to iron which is invariably present 
to some extent in the ingredients used, and, of course, 
the more iron there is as an impurity the more must 
be the amount of manganese dioxide added. Thus in 
some cases, in order to obtain the full green fluor- 
escence, an appreciable quantity of iron must be added 
to relatively pure ingredients so that the necessary 
quantity of manganese may be incorporated in the 
glass, the iron being needed to correct the amethyst 
colour which so much manganese would otherwise 
impart to the glass. 
This procedure appears to impair the working 
qualities of the glass to some extent, and it is found 
that glass of a quality superior (in respect to its 
behaviour in the flame) to that usually employed can 
be made if iron and manganese are avoided. A few 
experiments may be mentioned in support of this 
statement. 
Glass made from pure materials shows practically 
no fluorescence, the feeble glow being of a grey-blue 
colour. A Rupert’s drop made from the same glass 
gives a similar feeble glow. 
A Rupert’s drop made from glass giving normally 
a strong green fluorescence shows only a slight grey- 
blue glow. After the tail of the drop had been heated 
to softening point this part showed the usual green 
glow. In a high vacuum under very intense bom- 
bardment there was an indication of some slight 
green glow on the drop. The drop was broken and 
the powdered glass gave the full green glow. The 
evidence was that only a very thin skin represented 
the part cooled quickly enough to give next to no 
fluorescence. 
Calcium silicates of varying composition containing 
a little manganese, which were fused by the oxy- 
hydrogen blowpipe, showed on the outside portions, 
' which appeared to be completely vitreous, no 


