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POPULAR SCIENCE REVIEW. 
argillaceous slates to the Silurian, passing gradually in their upper portion 
into the Devonian.’ 
In going through this volume, one cannot hut sympathize with its 
author, who states (p. 397) that he feels ashamed when he thinks ‘how 
German mining engineers may read the reports of some of our mine captains 
and experts on mineral properties.’ We would add that we are by no means 
satisfied that the opinion of foreigners, with regard to English mining 
literature, will be materially improved by a perusal of the book before us. 
It is, however, probable that the information vouchsafed (p. 417), namely, 
that ‘ potash is potassium mixed with varying proportions of other substances,’ 
will be new to them. 
DOUGH WAYS MADE SMOOTH* 
T HIS is another of the volumes of interesting essays for which Mr. Proctor 
is becoming famous, there being few authors gifted with his wondrous 
power of making interesting and instructive articles out of some of the most 
difficult branches of science. Like most of the preceding volumes, Rough 
Ways made Smooth, is essentially a collection of some of the numerous 
articles contributed by him to the magazines during the last few years. We 
note, however, that many of them have been revised and amended so as to 
render them more suitable for their present purpose. The present volume 
commences with an essay on the ‘ Sun’s Corona and his Spots,’ in which the 
author shows that the theory that the corona varies in size directly as the 
number of spots, is without adequate basis, although several of those who 
have devoted much attention to this subject were led to suppose that it did. 
The second essay is on ‘ Sun-spots and Commercial Panics,’ and is devoted to 
showing the fallacy of the idea that sun-spots rule the commercial morality 
of civilized nations. The idea of a possible connection between sun-spots and 
commercial panics is founded on one of those partial coincidences which are 
eo fascinating to the minds of the quasi-scientific, or to even savants, when 
they sally out of their own domains into less familiar regions. 
The third essay, ‘ New Planets near the Sun,’ deals in a popular manner 
with the observations of .Prof essors Watson and Swift during the eclipse of 
July 1878. The fifth and sixth essays deal with the Moon, and have special 
reference to its past history and the supposed new crater. There are one or 
two errors in these, not so much on the part of the author, as on the part of 
those whose opinions are quoted. The early history of the Moon, like the 
early history of the Earth, must be discussed by one having the combined 
resources of chemistry and mathematics at his command. Any discussion by 
one who is purely a chemist, or purely a mathematician, must inevitably be 
vitiated by errors due to an imperfect grasp of the chemical or mathematical 
side of the problem. In several places, Professor Newcomb’s opinion is 
quoted on selenographical subjects, although the experience of that eminent 
astronomer must be most limited in these matters. Essays seven and eight 
* Rough Ways made Smooth. By Diehard A. Proctor. 8vo. London : 
Chatto and Windus. 1880. 
