384 
winds being to westerly as § to 3—a relation which could 
not hold if prevailing winds in this region were westerly. 
At Copenhagen the direction is S.S.W. In accordance 
with these facts the rainfall of the west of Scotland is 
much greater than that of the west of Norway. 
Mr. Laughton maintains that there is, throughout the 
sea, no trace whatever of the air being drawn in to any 
place of greatest heat, &c. (p. 303), and adduces many 
instances in support of this opinion; but, curiously 
enough, every case adduced confirms the opposite view. 
This arises from a misapprehension of the principle 
involved in Buys Ballot’s Law of the Winds, which may 
be thus put: Winds flow in towards the space where 
pressure is weak, vorticosely, so that in the N. hemisphere, 
standing back to the wind, the weak pressure is to the 
left. To take one case as an illustration :—Because the 
winds at Aden and south of Arabia do not blow directly 
in upon the heated sands of that region, but blow from 
W.S.W., it is concluded that there is no trace whatever 
in this part of the sea of the heated air influencing the 
winds. Now, if it bethe case that there is at this season 
a weakening of the pressure by an ascending current of 
heated air from the surface of Arabia, then, according to 
Buys Ballot’s law, the direction of the wind ought to be 
what observation shows it is, viz. W.S.W., and the more 
powerful the ascending current, the stronger will be the 
W.S.W. winds on the surface. 
Mr. Laughton regards itasestablished presumptively that 
a westerly upper current everywhere prevails (p. 97). This 
he has shown generally to be the case as respects upper 
currents of tropical regions and a portion of the United 
States, but not as respects other parts of the globe. The 
explanation of these upper currents iseasy. If the pressure 
of the atmosphere, at a uniform height of say, 10,000 feet, 
were ascertained, the highest would be immediately over 
the belt of calms, and the lowest over those regions where 
the mean temperature of the whole stratum, 10,000 feet 
thick, happens to be the lowest ; this result being a simple 
consequence of the increased tension of air by heat, and 
diminished tension by cold. Sincethe pressure at the height 
supposed will continually diminish on receding from the 
Equator on either hand, it follows from Buys Ballot’s 
Law that the prevailing upper currents ought to be 
westerly within the tropics, or, stated more exactly, W. 
by S. north of the Equator, and W. by N. south of it. It 
is during the winter months that westerly upper currents 
prevailin the United States. Since during this season 
the mean temperature rapidly sinks in advancing north- 
wards over America, atmospheric pressure will be much 
weaker over British America at a height of 10,000 feet 
than over the United States, and hence by Buys Ballot’s 
Law the upper current of the United States ought to be 
westerly. It may be remarked that since westerly upper 
currents are flowing towards colder regions, condensation 
of their vapour into cloud must frequently take place, thus 
rendering them visible ; whereas since easterly currents 
flow towards warmer regions, condensation will seldom 
take place, and hence they must frequently flow past 
unobserved, 
The broad zone included between latitudes 30° N. and 
S. comprises half the superfices of the globe. Over by 
far the greater portion of this zone winds are easterly, 
there being no season when any approach to a pre- 
NATURE 



[March 16, 1871 

ponderance of westerly winds is apparent. When to these 
are added the easterly winds in extra-tropical regions, 
already referred to, a predominance of easterly winds in the 
north of Siberia and in the east of Australia, in their 
respective summers, and in a large part of the Arctic 
regions at all seasons ; and though not a predominance 
yet the frequent occurrence, of easterly winds in the S. 
hemisphere, south of latitude 50°, it is plain that if there 
can be a preponderance of westerly winds over the globe 
viewed as a whole, it cannot be very great. A. B, 

THE SEWAGE QUESTION 
The Practical Solution of the Great Sewage Question, 
by a Combination of the Irrigation and Precipitating 
Processes. By William Justyne. (John B. Day.) 
N this little book the author tries to show that the 
ABC process is the only one which promises any 
hope of success among the methods which have been pro- 
posed or adopted for purifying sewage and utilising its 
valuable manurial constituents. ‘‘ Miscellaneous schemes,” 
including the dry-earth system, Liernur’s process, and 
all the precipitation plans, except the favoured one, are 
dismissed very summarily, and the irrigation system is 
made to look as unsuccessful and as dangerous as its op- 
ponents have ever represented it to be, while the immense 
weight of indubitable facts and evidence on the other side 
is entirely passed over. 
Then the ABC process is minutely described, and the 
scientific public is asked to believe that sewage, which 
contains suspended and dissolved organic and inorganic 
matters, and the chief value of which consists in the large 
amount of dissolved nitrogen, especially in the form of 
ammonia, which it contains, can be so purified by precipi- 
tation with a mixture of alum, blood, clay, animal charcoal, 
and what not, as that the effluent water shall contain no 
putrescible matter, and that the Preci~itate shall contain 
the manurial constituents ! 
What we do know with regard to the A B C and all 
other precipitating processes is, that they none of them 
separate out anything like all the dissolved (few of them 
nearly all the suspended) organic matters, and that the 
ammonia is necessarily all lost in the effluent water ; in- 
deed, several of these processes have been known actually 
to increase the amount of ammonia in the effluent water, 
by decomposing some of the organic matters. The only 
precipitating process which had the merit of attempting 
to throw down the ammonia was the phosphate process, 
which has been tried and abandoned so many times in 
this and other countries ; the reason of its failure was very 
simple : the ammonio-magnesian phosphate which it was 
expected would be found in the precipitate, requires an 
excess of ammonia in the solution to render it at all in- 
soluble, so that if any of this salt were contained in the 
sediment it would merely show that the effluent water still 
contained an excess of ammonia. ; 
We must comment especially upon two points in which 
a person seeking for information is likely to be misled as 
to matters of fact by consulting this book. On page 17 
we observe a table of the average percentage composition 
of solid and fluid human excreta, from which one might 
easily be led to suppose that the solid is more valuable 
than the fluid (as it is weight for weight), but we nowhere 
