1875.] Notices of Books. 255 
of information, and discusses sun-spots, nebulz, and multiple 
stars, while it further makes clear to us the meaning of such 
terms as ‘polar distance” and ‘right ascension.” The 
language throughout is of the clearest; the book is well 
illustrated, and the author has throughout described simple 
experiments to illustrate his meaning. By using a moderator 
lamp to represent the sun, an orange with a knitting-needle 
stuck through it to represent the earth, a tub of water with 
floating balls, a small suspended ball, a round table with a ball 
placed in the centre, and a few simple contrivances of this 
sort, a number of important phenomena are made clear to the 
learner. The following is an example of the author’s style :— 
‘‘Thus, besides the planets, there are other members of the 
system, namely comets and falling stars, which will be mentioned 
again more fully hereafter. All these bodies form a sort of 
family having the sun for their head, and on Plate II. will 
be seen a view of this system as it would appear when looked at 
from above; but it is impossible thus to give an idea of the true 
scale of the system. In order to do this, take a globe a little 
over two feet in diameter to represent the sun: Mercury would 
now be proportionately represented by a grain of mustard seed, 
revolving in a circle 164 feet in diameter; Venus, a pea, in 
a circle of 284 feet in diameter; the earth also a pea, at a 
distance of 430 feet; Mars, a rather large pin’s head, in a circle 
of 654 feet; the smaller planets by grains of sand, in orbits of 
from 1000 to 1200 feet; Jupiter, a moderate-sized orange, in 
a circle nearly half-a-mile across; Saturn, a small orange, ina 
circle of four-fifths of a mile; Uranus, a full-sized cherry 
or small plum, upon the circumference of a circle more than a 
mile and a half; and Neptune a good sized plum, in a circle 
about two miles and a half in diameter.” 
Introduction to Experimental Physics, Theoretical and Practical; 
including Directions for Constructing Physical Apparatus, 
and for Making Experiments. By Apo.teH F. WEINHOLD, 
Professor in the Royal Technical School at Chemnitz. 
Translated by Benjamin Loewy, F.R.A.S. Preface by 
G. C. Foster, F.R.S. London: Longmans, Green, and Co. 
1875. 
In the Preface to this work, Professor Foster says:—‘*I am 
convinced that the true way to make the somewhat abstract 
notions necessarily encountered at the outset of the study of 
physics intelligible to beginners, is not to emphas‘z2 the abstrac- 
tions, but to provide the learner with the clearest possible ideas 
of the concrete facts from which the abstractions are derived. 
In any sound system of teaching, particulars must come before 
VOL. V. (N‘S.) 2K 
