268 
NATURE 
ment but of fact; mo one who examines the actual 
fragments and sees how precisely the edges of these 
bones fit one on to the other can refuse to admit that 
the parieto-temporal angle of Dr. Smith Woodward’s 
restoration is a genuine peculiarity of this skull. If 
this is admitted it becomes impossible to tilt the upper 
margin of the parietal upwards and outwards. In 
other words, this peculiar articulation of the temporal 
bone affords confirmatory evidence of the proper loca- 
tion of the middle line. 
It is a very interesting fact that the curious con- 
formation of the temporal region of the brain, to 
the reality of which Prof. Keith objects, is quite 
analogous to that exhibited in the remarkable cranial 
cast of the Gibraltar skull, of which he is the custo- 
dian, and in some of the casts of primitive crania 
(negro, Australian, and Tasmanian) which he kindly 
obtained for me. 
The greater part of Prof. Keith’s letter deals with 
the lack of symmetry in the original reconstruction, 
which was due to a slight error in the positions 
assigned to the occipital and right parietal fragments. 
The need for this correction was realised before the 
meeting of the Geological Society last December; and 
this was taken into consideration when I was writing 
my preliminary note. G. Exv.ior SMITH. 
The University of Manchester. 
*€ Aéroplanes in Gusts.’’ 
I SHALL esteem it a favour if you will spare a little 
space in which to refer to the unsigned review of the 
first edition of my book, ‘‘Aéroplanes in Gusts,” 
printed in Nature of October 2. 
It is not at all my intention to refer to or contest 
an adverse opinion standing alone, but there is asso- 
ciated with that opinion, in a way that might appear 
to justify it, a misstatement of fact that I can scarcely 
be expected to pass without an endeavour to correct. 
Your readers are informed that I ‘‘measure the 
effect of a gust of wind by the accelerations of the 
air particles relative to the aéroplane.”” That I cer- 
tainly do not do, and your reviewer has no excuse 
whatever, in anything I have written, for attributing 
to me so simple and foolish an error as the words 
imply. A most casual reading of my book, even in 
its first pages, shows, decisively, that I quite properly 
measure the gust—not “the effect of a gust,’’ whatever 
that may mean—by the acceleration of headway, or 
acceleration of the velocity relative to the air, which, 
independently of that due to gravity and even of that 
due to the propeller, is being impressed upon the 
flying machine by the air. 
The confusion made possible by not maintaining or 
exhibiting, as I have done in my book, the distinction 
between an actual acceleration and an impressed 
acceleration, and by not excluding the gravitationa 
acceleration, scarcely needs enlarging upon or explain- 
ing in the columns of NATURE. 
S. L. Wa kpEn. 
Muswell Hill, N., October 4. 
I HAVE just received the second edition of ‘ Aéro- 
planes in Gusts,” and in reply to the author’s criticism 
of my review, I cannot do better than quote the 
passage on p. 2 containing the definition :— 
“Using therefore the term ‘headway’ in place of 
the cumbersome ‘ velocity relative to the air,’ it will 
be taken for granted that the reader knows that :— 
‘“(1) The instantaneous strength of gust at any point 
of the air as regards a given flying-machine flying 
at that point is measured by the acceleration of head- 
way which any singularity of the air at that point is 
impressing upon the flying-machine, and the direction 
NO. 2296, VOL. 92| 
[OcToBER 30, 1913 
of the gust is opposite to the direction of the impressed _ 
acceleration. — , 
“For example :—If the air is accelerating down- 
wards at qo ft. p.s. p.s., it is impressing upon the 
flying-machine an upward acceleration of headway of 
40 ft. p.s. p.s., and this is the measure of the down- 
ward gust. In other words, the gust is of strength 
4o ft. p.s. p.s., downwards. Simple velocity as dis- 
tinguished from rate of change of velocity is, it will 
be noticed, completely ignored.” 
(The author then goes on to point out that accelera- 
tions may be represented by straight lines. Agreed.) 
On p. 4 he says :— 3 
“The general method of finding the impressed 
accelerations acting at a given instant upon a flying- 
machine consists in first answering the question :— 
“Tf at any given instant the flying-machine could 
be suddenly transformed to a small smooth concen- 
praise mass, how would it accelerate relative to the 
air: 
‘The acceleration answering the above question is 
the ‘resultant relative gravity’ of the following dis- 
cussion, and when common gravity is subtracted in 
vector sense the result is the acceleration tendency or 
impressed acceleration due to the gusts. When from 
this result the impressed acceleration due to the abso- 
lute acceleration of the air at the place of the flying- 
machine is also subtracted in vector sense there will 
usually be found an impressed acceleration remaining. 
This is due to the air having what is called ‘‘ velocity 
structure’’ at the point, and to the flying-machine 
in crossing that structure creating for itself a rate of 
change of headway.” 
If Mr. Walkden considers that he has received any 
injustice through the use of the term “effect of a 
gust” in substitution for his reference simply to “a 
gust,’’ or the measure thereof, 
“effect "’ should certainly be withdrawn. But as re- 
gards his views on ‘impressed accelerations,’ the 
above quotations will probably appeal to readers of 
Nature far more effectively than any criticism, how- 
ever adverse. Yet several journals have reviewed the 
book favourably, and it has run into a second edition. 
THE REVIEWER. 
Mass as a Measure of Inertia. 
Can any of your readers enlighten me as to the 
authorship of the definition, ‘‘The mass of a body is 
the dynamical measure of its inertia”? JI am under 
the impression that it is due to Clerk Maxwell, but — 
have not been able to find where it occurs. I should 
be grateful for information as to where to look for 
it. W. C. Baker. 
School of Mining, Queen’s University, 
Kingston, Ont., October 13. 
ENGINEERING RESEARCH AND 
COORDINATION. 
| ee questions of the coordination and encour- 
agement of research in engineering have 
been brought forward in various ways recently. 
In April Sir Frederick Donaldson, chief super- 
intendent of Woolwich Arsenal and president of 
the Institution of Mechanical Engineers, referred 
to them in his presidential address. At the 
recent summer meeting of the same institution 
held in Cambridge, Mr. G. H. Roberts, of Wool- 
wich, read an interesting paper entitled “A Few 
Notes on Engineering Research and its Coordina- 
tion,” while the matter was also touched upon 
ITS 
the reference to — 
