Marc ITI, 1915] 
NATURE 
6) 


attitude, and largely accounts also for the perpetual 
success of those whose business it is to defy the sec- 
tion and to maintain their ‘“‘ unworked”’ patents to the 
detriment of the British industry. 
Justin E. Porrak. 
London, March 4. 

Measurements of Medieval English Femora. 
Pror. Kart PEARSON’S criticisms are always wel- 
come and stimulating to those strong enough to bear 
them though, since they are usually of the destructive 
variety, the fear of them undoubtedly prevents a good 
deal of work which would add to our knowledge being 
published. Let me deal, for instance, with the follow- 
ing criticism. “Looking at Dr. Parsons’s results I 
can but conclude that his sexing is based on a fallacy, 
and the dip he has created in the Rothwell femora 
between those with 45 and 47 mm. heads—the range 
of Dwight’s doubtful sex—is due to conscious or uncon- 
scious selection of his material; out of the great masses 
of bones available at Rothwell (which should have 
occupied in measurement of many characters and in 
their adequate reduction the whole time of a man for 
_ four or five years).”’ 
By ‘‘coascious selection of material’ I can scarcely 
think that deliberate fraud is suggested not 
indeed know what it really means; W hile unconscious 
selection I suppose is covered by inaccurate measure- 
ments or by the absence of bones of a certain size 
which ought, mathematically, to be there. 
At any rate, the impression conveyed by the stricture 
is that, from an enormous available mass of material, 
I have deliberately or unfortunately picked out a small 
selection which would bear out some object which I 
wished to prove 
It is almost inconceivable that Prof. Karl Pearson 
would have mentioned the “creat masses of bones 
available ’’ unless he really knew what he was talking 
about, so that we may safely assume that he has been 
to Rothwell and satisfied himself on this point. 
I can only say that I have spent a great deal of 
time at Rothwell, and that I found considerable diffi- 
culty in picking out 300 measurable femurs, and this 
was particularly the case with the slighter bones w hich, 

owing to the damp, snapped like carrots when 
touched. 
I can assure Prof. Pearson that every measurable 
bone which could be extricated was welcome, and 
none were rejected because their sizes did not suit. 
As to four years of a man’s whole time being needed 
for the research, I can only infer that Prof. Pearson 
thinks that there is unlimited measurable material at 
Rothwell, and that, if I could not give the time he 
thinks necessary, I had better have left it to some 
other man who could. These really are the words of 
the ‘‘mere mathematician’’ ignoring all practical 
details. Did not Prof. Pearson observe when he went 
to Rothwell that the bones were rotting with damp— 
exactly the opposite condition, by the bye, to his 
Naquada bones—and that the farther he worked into 
the stack, for he must have done this or how would 
he otherwise have known about the “great masses 
of bones available’’? the more sodden and useless 
the material became? As no one else showed the least 
sign of spending even four weeks in working at the 
Rothwell bones, I did what I could while I could, for if 
I had left it for another ten years the available mate- 
rial would have been much less. Incidentally, I ad- 
vised the restacking of the heaps, so that air now 
gets among the bones, and they will not disintegrate 
so rapidly. There is another practical point, too, about 
which Prof. Pearson is silent; it is the fact that the 
ordinary anatomist has difficulty in getting unlimited 
measurements recorded, and my contribution of six- 
NO. 2367, VOL. 95] 
| 
teen sets of measurements on nearly 300 bones was all 

; means of reducing the brig 
I could fairly expect our journal to print for me at 
one time. 
In other points I think that Prof. Pearson and I 
are in practical agreement. We agree that neither of 
us can sex femurs with accuracy (I find that in 
eighty-two attempts I made seven mistakes), but that, 
when we have sexed them to our individual taste, the 
average difference in results is a fraction of a milli- 
metre. We both agree that the head measurement 
alone is often liable to mislead, and that a series of 
secondary sexual tests of graded value are needed. 
These I have attempted to provide in a paper which 
will appear shortly, and of which I will not fail to 
send Prof. Pearson a copy. 
Above all, I am glad to see that he tacitly agrees 
with me about the Rothwell bones being medieval, 
probably of the fourteenth and adjacent centuries. 
F. G. Parsons. 
Salis 
St. Thomas’s Hospital, 
The Green Flash. 
Pror. Porter’s interesting letter (NATURE, February 
18, p. 672) on this subject must be my excuse for 
sending a summary of my own experience during 
the last eighteen years in which I have observed 
the flash more than a hundred times, and in no 
single case did I find anything not explainable by 
atmospheric dispersion, nor anything that could be 
put down as a subjective or complementary after- 
image. 
I may add that I have observed with the naked 
eye, with an opera-glass (power 3), with binoculars 
(power 9), and with a telescope (power 100). 
Whenever on a clear day a low sun is observed 
through a telescope, the upper limb appears bordered 
with a marine, i.e., blue-green, fringe, the lower with 
an orange-red fringe, the side-limbs are unaltered. 
(The telescope should have a solar diagonal and other 
rhtness of the sun.) 
upper fringe develops ultimately into 
the green flash, the blue element weakening as the 
sun descends. I have watched this change with the 
telescope, and it is perfectly continuous. 
Again, if the sun descends behind a low cloud, 
parallel to the horizon, but with a clear space between, 
the base of the sun, just as it becomes visible, shows 
the red flash. I have seen this only thrice, as the 
necessary conditions are obviously seldom satisfied. 
The red flash seems inexplicable save by dispersion. 
Under favourable conditions at sunset, as the upper 
segment of a yellow sun gradually diminishes, the 
right and left corners of the segment become green; 
this colour gradually spreads inwards, becoming 
marine, until finally the last tip of the sun may 
appear almost greenish- blue, and just as the sun has 
sunk, a very faint wisp of blue light is glimpsed 
directly above the point of disappearance. One friend 
even records a violet wisp. 
But when the sun is orange the blue is replaced 
by green, and when the sun is really red no green 
The marine 

flash at all is seen, the atmosphere cutting off the 
green as well as the blue rays. To see these changes 
it is desirable to use a power of 8 or 9. 
Prof. Barnard, writing to me some years ago, said 
he preferred the title, ‘blue flash,” as in sunsets seen 
over the Pacific from the Lick Observatory the final 
flash was usually blue. Doubtless this is due to clear 
atmosphere. ; 
It is well known that at sunrise, when no exciting 
colour can be present, the flash has been seen, some- 
times green, sometimes blue. 
In the rg06 volume of Symons’s Meteorological 
