Nov. 24, 1881 | 
NATURE 
77 
ken in this book.” The Second Law of Motion is given 
in the imperfect Whewellian instead of the perfect New- 
tonian form, in which all the best treatises on dynamics 
have given it since the salutary return to Newtonian pre- 
cision was inaugurated by Thomson and Tait. On p. 198 
the author proposes to measure gravity on an Atwood’s 
machine, with a falling mass of one centigramme. Did 
he ever try the experiment? On p. 241 the student is 
told that the Torricellian vacuum is to be found in the 
space left by the mercury at the top of a ¢hermometer | 
Under the heading of Calorimeters (which instruments, 
by the way, are nowhere described) the novice is informed 
that ‘‘ Joule established the fact that 772 pounds of mass 
falling through one foot give out a_thermal unit” ; from 
which it would appear that heat is the product of a mass 
into a length. Bad as this is, it is pardonable beside a 
passage in the introductory part of the beok (p. Io), in 
which the reader is assured that a force generates heat at 
the point of its application when the point of application 
does not move forward. One grows weary of gathering 
from the rank crop of blunders ; but a final example—the 
very last sentence of the book—shows the accuracy of 
our author’s physical knowledge as displayed in his theory 
of dew. ‘A tarpaulin spread over the ground, or nature’s 
tarpaulin of clouds, will veffect the radiating rays (sic) of 
heat, and under the tarpaulin or clouds dew is not 
deposited.” 
“Let me start,” says Dr. Aveling (p. 6), “with two 
truisms—(1) That no book is worth reading that is not 
worth analysing; (2) that the ideas enunciated by a 
teacher, either by voice or pen, are not thoroughly the 
ideas of the learner until they have been expressed again 
in his own words. If, therefore, that which I am about 
to write is in any sense useful, it will be worth the while of 
the student to make analysis thereof.” What if the 
student’s analysis throw unexpected light on the first of 
these truisms ? ie JF 40h 
Der Volkergedanke im Aufbau einer Wissenschaft vom 
Menschen, und seine Begriindung auf ethnologische 
Sammlungen. (Berlin, 1881.) 
Die Vorgeschichte der Ethnologie. (Berlin, 1881.) 
THESE two pamphlets, by Prof. Adolf Bastian, are written 
to promote the doctrine he is never weary of teaching, 
that the scientific method of studying man is the museum- 
method of collecting and classifying his results, whether 
these be weapons or idols, or myths or superstitions, or 
what not. When ina group of such things there comes 
into view a common principle or thought, this is a Volksge- 
danke, a manifestation of the popular mind, a definite 
something for the science of man to occupy itself about. 
It was the desire to get at such general principles of 
human action that led the late Prof. Waitz to compile his 
Anthropology, and Prof. Bastian has gathered, in the 
many volumes he has published, an even vaster museum 
of human facts. In the first-named of the two publica- 
tions above, the reader will find collections of evidence as 
to many of the problems which are now occupying the 
minds of anthropologists, such as the primitive relations 
of the sexes, the development of the family and of pro- 
perty, and the belief in ancestral and patron spirits. The 
few lines of comment with which the author links toge- 
ther his pages of citations are of especial value, as giving 
his judgment of the meaning of the facts. In the second 
pamphlet the author traces the growth of anthropological 
museums out of the old cabinets of curiosities. Neither 
treatise is well suited to quote passages from, as these 
lose their- value when disconnected from the rest, like 
single specimens taken out of the museum. Now and 
then Prof. Bastian makes a sort of holiday digression, for 
instance where he collects page upon page about modern 
European miracles, relics, and pilgrimages, about which 
he truly says, “the nature-peoples, with their rude, clumsy 
fetishes, are no match for the subtleties of super-refined 
civilisaticn ” 1D 18}; Ae 
LETTERS TO THE EDITOR 
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Telescopic Definition in a Hazy Sky 
THE diminution of star disks during temporary haze or even 
by a thin passing cloud has been particularly noticed by Sir 
John Herschel. The effect of this haze is apparently to 
diminish the intensity of diffraction phenomena, The mark- 
ings on the full moon have never been seen so blackened and 
distinct as through the haze of a London fog. On one occasion 
a very gentle east wind brought down a London fog to Reading, 
That evening the air was extremely still, but embrowned with the 
haze. Castor bore a magnifying power of 600 with a Wray 53 achro- 
matic. The object-glass was being adjusted to the axis of the 
tube. Finally an intense jet black ring was seen to surround 
each star of this celebrated double, supplemented with one 
bright perfectly defined diffraction-ring, then a fainter ring at a 
further distance could be descried. The perfection of this de- 
finition has never since been attained. The haze had setiled down 
into still air. The eastern breeze had died away. The brown 
fog remained in the sky ; diffraction assumed its most perfect 
form. The moon bore any power J could muster with 
absolutely steady definition. These states of the atmo- 
sphere are extremely rare. I can now record a repetition 
of this wonderful steadiness. On November 9 Col. Abadie, 
Mr. Maunsel, and myself, were observing Saturn with an 8% 
Calver mirror. The crape veil and belts were well shown 
with the pale blue Polar cap. Ball’s division was intensely 
black, The outer ring was narrow, and its dark grey tint con- 
trasted strongly with the brilliant whiteness of the inner ring. 
I was greatly a-tonished, however, to descry Encke’s division 
on the outer ring usually called A. The shadows of the ball 
were well marked. The eastward shadow much stronger than 
the western. A very brilliant narrow band edged the northern 
belt near the plane of the rings. The inner edge of the ring B 
projected a thin shadow on the ball. A lady who had no pre- 
vious knoy ledge of the belts, entering the observatory last night, 
said they appeared to consist of several fine lines of parallel 
bands separated by very fine brighter bands. At II p.m. there 
was a very wide narrow halo round the moon, Saturn appear d 
much bedimmed, and Jupiter shorn of his brilliance. Yet 
Col. Abadie writes : ‘‘ Jupiter was a sight to be remembered. 
The distinctre-s of all the belts was enhanced by bright zones ; 
one to the north of the uppermost belt was particularly to be 
noticed. The clouds between the equatorial belts changed in 
appearance from being very fleecy to a long wavy appearance” 
(we were observing about three hours), The moon was too dim 
for observation. Encke’s division is so seldom seen in my expe- 
rience, its appearance in the field of so small a telescope was a 
matter of great surprise ; and but for the concurrent testimony 
of two others for about a space of three hours, I certainly 
should have greatly doubted the accuracy of the observation 
At all events, it is a valuable demonstration of the value of the 
chiaro-oscuro in astronomical research. 
Eastbourne, November 16 G. W. RoystTon-PIGOTT 
The Morteratsch Glacier 
DuRING my stay in the Engadine this summer I took the 
opportunity of making a few observations relative to the move- 
ment of the Morteratsch Glacier, which may he of interest to 
some of your readers. ‘These observations were taken zszde the 
artificial cave of the above glacier in preference to the surface, 
as I thercby obtained a more direct measurement with a fixed 
point, as will be shown presently, and greater protection for the 
provi-ionary stations, made in the ice, against disturbances of 
fluctuating temperatures or the curiosity of visitors, The 
arrangement was very simple, namely: in the roof of the 
cave 2—} in. round staves 2 feet long were fixed, at a 
relative angle of 45°, in sucha way, that they prevented each 
other from dropping out, and were further clamped to- 
gether by a small metal band, from which a plumb-bob was 
