360 
NATURE 
| Feb. 16, 1882 
newest-published text-books of the science is being 
bought by the public at the rate of a thousand copies a 
month. Under these circumstances it would be remark- 
able if all the works put before the public were of equal 
scientific merit, for such a demand cannot but tempt into 
the field the semi-scientific bookmaker who is ever ready 
to produce something to meet a popular taste. The work 
before us must, we fear, be classed with the semi-scientific. 
Its authors, so far as we are aware, are gentlemen who 
have yet to make their mark in the scientific world, and 
who, though not ill-informed in a general kind of way as 
to the applications of the science, cannot be said to have 
added by their present work to the scientific knowledge 
of the subject. The work opens with an account of the 
history of lighting in general from the days of Greece 
and Rome; and it devotes no inconsiderable part of its 
pages to the early history of electric lighting. We ob- 
serve, by the way, that the authors fall into the error of 
putting Davy’s discovery of the voltaic arc so late as the 
year 1813, when he experimented with his large battery 
ef 200 cells. But he had discovered the arc at least nine 
years before that date. The manufacture of carbons for 
electric light claims half a dozen pages. Not too much 
when there is so much dependent on the quality of the 
carbon, and when carbons areas bad as they are. But we 
were not aware that those of M. Napoli were so superior 
to all others as to deserve a monopoly of description. 
The process of covering the exterior of the carbon-rods 
with an electrodeposited coating of copper is stated by 
the authors to have been first adopted in 1875 by M. 
Reynier, whose semi-incandescent lamp and modified 
Daniell’s battery are described in effusive detail, though 
neither of these inventions can be said to be of capital 
importance. The chief feature in the book is that part 
which deals with the various systems of electric incan- 
descent lamps. These are described very fully and with 
copious illustrations. The authors appear to prefer the 
system of Edison, for whom they have a great admira- 
tion, of whom they give a portrait (an honour shared by 
M. Gramme only), and concerning whom they narrate very 
naively several gossipy tales—how he and his assistants 
were nearly poisoned by mercury vapour when they first 
tried to work Sprengel pumps, and how he sent an expe- 
dition south for the metal thorium. The section devoted 
to dynamo-electric machines is also well illustrated, and 
fairly descriptive, though the style of exposition is of the 
“popular” order. The work concludes with a notice of 
the application of electric light to lighthouses, to naval 
and military warfare, and to the stage. With respect to 
the first of these applications, the authors attribute to 
Fresnel the application of dioptric lenses to lighthouses. 
Is it ignorance, or is it patriotic bigotry that is to blame 
for their obliviousness of the fact that Brewster suggested 
this very application in 1812, ten years before Fresnel, 
and that in 1820 he had already taken steps to urge the 
matter upon the notice of a too deliberate officialism ? 
Many excellent woodcuts adorn the pages of the work of 
MM. Alglave and Boulard, which will doubtless make it 
a welcome book for many a library table where popular 
science is in request. 
An Elementary Treatise on the Tides based upon that of 
the Late Sir J. W. Lubbock, Bart. F.R.S.; to which is 
added a newly-devised Method of Computation of the 
Heights of High Water at Liverpool, with Factors for 
other Ports, and Tables adopted by the Admiralty. By 
James Pearson, M.A., F.R.A.S. (London: J. D. 
Potter ; Fleetwood: W. Porter and Son, 1881.) 
Tus Treatise on the Tides, by the Rev. J. Pearson, 
M.A., F.R.A.S., contains an interesting historical sketch 
of tidal theories, extending from an early period to 
the present time ; and while referring to the slow 
progress made in our knowledge of tidal phenomena, 
assures the inquirer of the interest attending the investi- 
gation. The researches of Newton, Bernouilli, La Place, 
and others, had gradually established a theory which, 
from the discussion of many observations made at ports 
in the United Kingdom by Sir J. Lubbock, brought into 
practical use a series of tables by which the times and 
the heights of high water at certain places, mainly on the 
shores of the United Kingdom, could be computed with 
an accuracy sufficient for the requirements of seamen, 
and others interested, especially the proprietors of docks. 
Based on the general results of Sir J. Lubbock’s labours, 
the author; from observations extending over several 
years, has introduced tables auxiliary to those heretofore 
employed, for computing the heights of high water at 
Liverpool, where the tides have occasionally the great 
range of thirty-three feet. The results of these predic- 
tions (as compared with observation) show that the course 
of the “ diurnal inequality ’’—previously disregarded—has 
by their aid been successfully traced. On the coasts of 
Great Britain generally, the diurnal inequality is not so 
important a factor as it is at Liverpool, at which place it 
amounts at times to one foot or more. The treatise 
cannot fail to be received with interest and to encourage 
attention to the subject. 
LETTERS TO THE EDITOR 
[The Editor does not hold himself responsible for opinions expressed 
by his correspondents. Neither can he undertake to return, 
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No notice is taken of anonymous communications. 
[The Editor urgently requests correspondents to keep their letters 
as short as possible. The pressure on his space is so great 
that it is impossible otherwise to ensure the appearance even 
of communications containing interesting and ncvei facts.| 
The Movements of Jupiter's Atmosphere 
The reference to the belts of Jupiter contained in my article 
on the geological activity of the tides (NATURE, vol. xxv. p. 213), 
was perhaps superfluous, for the subject is only collaterally 
connected with the points there under discussion ; but as Mr. 
Mattieu Williams has commented on what I said, I should like 
to make a few remarks on his letter. Notwithstanding what he 
says I am stillinclined to hold that the time-honoured explanation 
of the belts of Jupiter is the true one. In that explanation the 
terms trade and anti-trade winds are, I conceive, used in a 
somewhat extended sense as a consequence of thermal causes, 
and without reference to the existence of a solid nucleus, a 
current is supposed to set upwards in equatorial regions and 
then to spread out into higher latitudes ; here the fluid has 
more moment of momentum than is adapted for the latitude in 
which it finds itself, and accordingly moves relatively to the 
subjacent matter in the direction of the planet's rotation, and 
forms an anti-trade wind. Conversely the trade winds arise 
from fluid moving into lower latitudes, when it has a deficiency 
of moment of momentum, Such an explanation seems to serve 
equally to explain the unequal rotation of the surface of the 
sun in different latitudes, and the Jovian belts. 
The trade and anti-trade winds are essentially a thermo- 
dynamic effect, and in my paper I expressed an opinion that 
they might be partly due to the heat of the Jovian nucleus, It 
seems to be generally assumed that the great rapidity of that 
planet’s rotation is a sufficient cause for the great violence ot 
the supposed trade-winds which produce the belts. But my 
chief object in referring to the matter was because rapidity of 
rotation is not a sufficient explanation, without a statement as to 
the mode of reinforcement of the thermodynamic causes. Now 
the great distance of Jupiter from the sun largely weakens those 
causes, and it seems to me that there are only two ways in 
which they can be strengthened, viz. first by the large amount 
of gas on which the solar radiation has to work, and secondly, 
by the heat of the nucleus. 
With regard to the deductions to be drawn from the low 
specific gravity of Jupiter, I may mention that in 1876 I pointed 
out that the observed ellipticity of the planet’s figure can only 
be explained on the assumption of great density of the central 
portions of the planet. Taking indeed the best data attainable, 
I showed that the mean density of Jupiter must be about 70 
times as great as the superficial density, if we follow Laplace 
