550 
NATURE 
[April 13, 1882 
letters on the early shekels and those on the Moabite 
stone, and on the inscription of Esmunazar, there is in 
the case of some letters on the copper coins of the 
Asmonzan family, which are regarded as being but a few 
years later in date, a marked divergence. This is notably 
the case with the letters 7,1,and w; and singularly 
enough these three letters revert to the forms employed 
on the silver shekels on some of the coins struck during 
the revolts, though the position of the letters is in some 
cases changed. Possibly the modification in the cha- 
racters is due to their being so much smaller on the 
copper coins than on the silver. The persistence of the 
Phoenician or, as it may here be called, the Jewish or 
Samaritan character, is well exemplified by the legend on 
the shekel. It is of course retrograde, or to be read from 
right to left. The legend stands £ FQWW LPW, 
but when reversed, and the position of some of the charac- 
ters slightly altered, it comes outas SPL “LEPAL, 
in which SOL ISRAL can at once be seen, especially by 
eyes to which the Greek = and P are familiar. 
Any notice of Mr. Madden’s book would be incomplete 
without some reference to the Roman coins struck in 
commemoration of the Conquest of Judea, of which 
excellent woodcuts are given. “ Beneath her palm here 
sad Judzea weeps,’’ while the captive warrior with his 
hands bound behind him, and his armour strewn upon the 
ground admirably typifies ‘‘How are the mighty fallen, 
and the weapons of war perished !”’ The sections devoted 
to money in the New Testament and to counterfeit 
Jewish coins will be read by many with interest, while 
the opening chapters on the early use of silver and gold, 
and on the invention of coined money, contain an excel- 
lent summary of our present knowledge. To the numis- 
matist a work like the present is of special value, but we 
think that the ordinary student who neither knows nor 
cares in the smallest degree for coins as tangible objects 
for study or collection, will find much to reward him for a 
perusal of the non-numismatic parts of the volume, while 
to the theologian, and especially to the student of Jewish 
history, much of the information here contained is almost 
indispensable. JoHN Evans 
THOMPSON'S LESSONS IN ELECTRICITY 
Elementary Lessons in Electricity and Magnetism. By 
Silvanus P. Thompson, B.A., D.Sc., F.R.A.S., Professor 
of Experimental Physics in University College, Bristol. 
(London : Macmillan and Co., 1881.) 
V E are glad to welcome a really admirable attempt 
to place before students the modern doctrines 
concerning electricity and magnetism in a popular but 
reasonably accurate form. The book begins with a rapid 
historical sketch of the long known facts on which it is 
the custom to dilate in every elementary text-book on 
electricity ; but the historical statements indicate by little 
additional details that they have not been simply copied 
from the joint-stock property of text-book writers, but 
that some original authorities have been referred to. 
This portion of the book occupies the first 190 pages, and 
it does not call for special remark; the illustrations are, 
as a rule, familiar ones, but there is a very convenient 
magnetic map of England for 1888 as a frontispiece ; and 
everything relating to the use of iron filings is well and 
clearly put, as would naturally be expected. The author’s 
statements of the well-worn facts are moreover interspersed 
with notes and characteristic touches which redeem them 
from dulness. 
The second half of the book commences in Chap. IV. 
with the principle of electrostatic measurement and the 
definition of potential, which the author proceeds to apply 
to various cases ; and he succeeds in giving the theory of 
attracted disk electrometers and of the capacity of con- 
densers in a way which it is very satisfactory to find in so 
small a book. It is in the possession of this more strictly 
scientific information that the book differs from its pre- 
decessors in the same line, and we think the author has 
shown much ingenuity in contriving to pack into so small 
a compass not only all the ordinary popularly known 
facts, but also a considerable amount of more advanced 
science, which will be most acceptable to teachers and to 
students, who have long been accustomed to a great gap 
between mere experimental treatises on the one hand, 
and advanced mathematics on the other. 
After the chapter on Electrostatics comes one on Elec- 
trodynamics and Magnetic Measurements, which is very 
well done, though necessarily too concise to be in all parts 
readily intelligible to a beginner. It contains a reference 
to Rowland’s convection experiment and to Hall’s effect. 
The chapter which follows, on Ohm’s law, is perhaps the 
least satisfactory in the book. We are not satisfied with 
the statement of Ohm’s law, nor with what is said con- 
cerning the meaning and measurement of resistance. 
Towards the end of the book comes a brief account of 
the Siemens’ and Gramme machines, of Planté cells, of 
telegraphs, telephones, and the electric light. There is 
also a chapter on “‘ Electro-Optics,’’ which refers to Dr. 
Kerr’s discoveries and to Maxwell's theory of light. 
If it is necessary to say anything by way of general 
criticism, it is that the author sometimes shows a disposi- 
tion to theorise a little too baldly, and to state without 
qualification, and with an air of certainty and completeness, 
views concerning the nature of electricity, which, though 
undoubtedly they have some truth in them, ze. which 
certainly are steps towards the truth, yet have no finality 
about them, and which require to be cautiously worded 
and expressed lest they should mislead. For instance, 
his statements in the preface that “electricity is not /wo 
but ove”; that, ‘‘ whatever it is, it is not matter and 
not exergy”, that “fit may be heaped up in some places 
and will do work in returning to its former level distribu- 
tion,” are all, considered strictly, unjustifiable dogmas of 
the kind we have mentioned. A student ought to be 
puzzled by the unqualified statement “that more elec- 
tricity can be made to appear at one place and less at 
another” when he has learnt from Maxwell that it always 
behaves exactly like an incompressible fluid of which all 
space is completely full. Neither are we altogether 
disposed to approve of the phrase “ Conservation of Elec- 
tricity,’’ by which the author seems to set much store. 
However, all these doctrines are immense improve- 
ments on the old forms of the fluid theory, and, being 
steps towards truth, will probably do far more good than 
harm. We are fully impressed with the necessity in teach- 
ing of getting some ideas into the heads of the students to 
begin with, and of polishing them up as much as possible 
afterwards. 
