324 
and with advantage to, the public. It is extraordinary 
how limited is the vocabulary of a large portion of even 
the well-educated section of the public; and it is the too 
free use of technical terms in the better class of popular 
natural histories which drives people to those of an 
altogether inferior description. Another point to which 
we would draw attention in connection with the ‘‘ Coral 
Guide” (which, by the way, includes sponges and various 
other low invertebrates) is the advisability of omitting 
the names of describers of particular species or structures. 
Such names as Wyville Thompson, Hickson, Duerden 
and Shipley are familiar enough to zoological students, 
but they are quite unknown to the outside public for 
whom the book is intended. 
A feature of the ‘Coral Guide” is the wealth and 
beauty of the illustrations, which render it a most won- 
derful shillingsworth, altogether apart from its high value 
as an excellent introduction to the groups of animals of 
which it treats. A number of new illustrations also 
characterise the seventh edition of the ‘‘ Mammal 
Guide,” which, for reasons apparent to those in the 
“know,” the present writer is debarred from either 
criticising or commending. 
TERRESTRIAL MAGNETISM. 
AS interesting paper describing the results of an 
investigation to determine to what extent magnetic 
disturbances of the needle are connected with the 
geological conformation of a selected mountainous 
district has recently been published.' 
The well-known inquiry into the relation between the 
magnetic and geological constitution of Great Britain 
and Ireland conducted by Riicker and Thorpe has been 
before us for some six years, and in the present paper we 
have the report of results obtained in another country 
and in later years having the same object in view. 
The region selected for the observations was the 
Kaiserstuhl, a mountainous district in the neighbourhood 
of Freiburg in Baden, of which exact topographical and 
geological surveys had been made, and it is from this 
source that the maps accompanying the paper and upon 
which the results of the observations are exhibited were 
obtained. 
The base station was at Freiburg on the spot occupied 
by Lamont in 1852, but the several observations were 
compared with a station nearly in the centre of the 
Kaiserstuhl, at which the magnetic elements were con- 
sidered normal. In all, 382 determinations of the 
horizontal force, 140 of the inclination and 137 of the 
declination were made, and the epoch assigned is 
1898°7, but no corrections for diurnal inequality were 
made. The resulting disturbances from these observa- 
tions are shown on a special map of “ Isanomalen.” 
The author arrives at the following conclusions :— 
(a) That wherever the geological conformation is of 
basalt, there he experiences disturbance of the needle 
partly due to permanent magnetisation of the basalt ; (4) 
that the principal disturbances are caused by compact 
masses of basalt with a North Pole acting vertically 
upwards—or nearly so—on the north-seeking end of the 
needle, and the magnetism of these masses is not due to 
induction from the earth. 
With (a) we may concur as to a connection being 
frequently found between the geological formation of 
basalt and magnetic disturbance of the needle, but it has 
been also shown that basalt may be present in large 
masses and certain forms without causing any such 
disturbance. The conclusion in (4) can hardly be 
accepted, for it is well known that in the northern hemi- 
1 - Erdmagnetische Untersuchungung im Kaiserstuhl,” von G. Meyer. 
(Published in the Berichte der Naturforschenden Gesellschaft zu Freiburg 
i. Br. Band xii., 1902.) 
NU. 1709, VOL. 66] 
NA TORE 
{JuLy 31, 1902 
sphere the north-seeking end of the needle is generally 
attracted downwards by locally disturbing rocks, pointing 
rather to induction. from the earth as the cause of the 
magnetisation of basalt. ° 
In order to find an explanation of the causes of the 
observed disturbances of the needle, pieces of basalt 
were taken from the surface and from a working quarry, 
and their several effects upon a compass observed, but 
no information of importance was’ obtained from the 
experiments. The question of the effects of lightning on 
the magnetism of rocks is also discussed, but dismissed 
as untenable. 
It should, however, be remarked that the author does 
not look for more than general results from the observa- 
tions as carried out, but they certainly form the nucleus 
of a further survey from which more definite results 
might be obtained as to the connection between geological 
conformation and magnetic disturbances. 
Having considered some of the effects of local magnetic 
disturbance in Germany, we may now turn to the 
remarkable effects of such disturbance on the magnetic 
declination in the United States as shown in the latest 
chart! of lines of equal value of that element for 1902. 
This chart is a continuation of the series published by 
the United States Coast and Geodetic Suryey, and gives 
true isogonals for every degree. An examination of the 
lines shows that some of the most remarkable disturb- 
ances occur in mountainous districts, especially in the 
State of California. With its lines of’ equal annual 
change of the declination this chart is decidedly valuable, 
both from the practical and scientific points of view. 
The values of the magnetic dip and declination given 
in Father Doyle’s pamphlet? are the result of eight 
years’ photographic record taken at the Manila Central 
Observatory during the period January 1, 1890, to 
December 31, 1897. _The position of this observatory 
has been specially selected with a view to avoiding 
magnetic disturbances either in the locality or the 
materials of the building. Curves of the mean hourly 
variation of the declination for each month of the eight 
years are given, and also curves of the’ mean annual and 
mean semi-annual variation of the dip and declination. 
The chief interest, however, of the data recorded lies in 
the values of the secular variation of both elements for 
the epoch 1887-99. In these we have corroborative 
evidence of the small secular change of the, declination, 
and the large change which is so marked in the dip, 
which has taken place during the epoch 1880-1900 at 
the observatories of Bombay, Batavia, Manila and Hong 
Kong. A chart of the isogonic and isoclinic lines corre- 
sponding to the epoch January 1892 for the region 
comprised between the Philippine Islands and Southern 
Japan is appended. 
THE “NATURE-STUDY” EXHIBITION. 
HROUGH the courtesy of the Royal Botanic 
Society, the aims of which are by no means so 
purely social as some of its present interests might sug- 
gest, a “ Nature-Study” Exhibition is now being held in 
Regent’s Park. Never has there been a better under- 
taking, nor could one be set on foot, which would do more 
to bring about a rational system of teaching such as is 
now looked forward to, whereby the pupils may be keenly 
interested instead of bored and their work made a labour 
of love instead of a dreary task. 
There have long been in this country those who appre- 
1 “Chart of Lines of Equal Magnetic Declination and Annual Change 
for 1902." (Published by the United States Coast and Geodetic Survey, 
February, 1902.) ‘ ‘ 
2.‘ Magnetical Dip and Declination in the Philippine Islands.” Brief 
notice of the same by Rev. John Doyle, S.J., of the Manila Central 
Observatory (1901). 
