NATURE 
161 
was u.founded. The great argument advanced against the 
use of graphic illustration has been that students would 
imagine that it was intended to convey the positions of 
tie ato as ia space, anl treir linking or binding to each 
other ; but in practice this has not been found to be the 
case. As s)01, however, as the pupils have become 
thoroughly familiar and conversaat with the use of 
symbolic constitutional formula, there is less necessity 
for the use of graphic formula, except, perhaps, in the 
case of complex isomeric organic bodies. 
The theory of the atomicity of chenical elements is 
also used throughout the book, and the author states that 
he his found it to b: remarkably coadacive to the quick 
and thorough understanding of chemical chaages. This 
theory is without doubt of great use in assisting the mind 
to generalise and grasp the numerous reactions of the 
elementary bodies, and by thus introducing this theory 
we are enabled to systematise to some extent the study of 
chemistry, and therefore to materially aid the memory. 
The illustrations are numerous and well executed, and in 
almost all instances give a very good idea of the kind of 
apparatus, which should be employed in the various 
experiments. In conclusion we think that if a student 
were to work conscientiously through this book he will 
secure a fair knowledge of elementary inorganic chemistry, 
which will serve as a suitable groundwork for him on 
which to found an extensive knowledge of this subject. 
We therefore cordially recommend this work to the notice 
of all teachers of practical chemistry. 
LETTERS TO THE EDITOR 
[ The Editor does not hold himself responsible for opinions expressed 
by his correspondents, No notice is taken of anonymous 
communications. | 
Periodicity of Rainfall 
THE remark of Mr. G. J. Symons in Nature, December 
26, that it seems to him ‘‘ more likely that the effect of cyclone 
is simply to alter the locality of deposition” of rain, suggests a 
doubt.whether the relation between rain and wind is sufficiently 
considered. The amount of evaporation must always be the 
chief element in the question of rainfall, and the total evapora- 
tion of any period must be much affected by the amount of 
wind. Evaporation may go on rapidly in still air, but it is 
almost necessarily increased if the air is moving. Storms over 
the sea not only bring moving air over a wet surface, but they 
also very largely increase the area of that surface by creating 
waves and foam. The evaporation during a cyclone may be 
presumed to be enormous. Wind in fact is almost always 
drying, even when rain is falling. 
May we not on this account see a theoretical probability in 
favour of Mr. Lockyer’s belief that the cycle of sun-spots coin- 
cides with that of rainfall ? 
If the solar spots indicate inequalities of temperature, the 
sun’s heat when they are numerous will be radiated in bundles 
of rays of unequal power. These we may suppose, being 
directly incident on different portions of the earth, will cause 
special barometric differences here. The result will be special 
winds, and therefore special evaporation ; followed by unusual 
rainfall. The locality of this extra rainfall will of course depend 
on other causes, partly on the direction of the special winds, and 
if it should be thrown on polar regions or any other part of the 
earth where it escapes observation, there will be an apparent 
failure in the cycle. This also seems not inconsistent with ex- 
perience as far as it goes ALBERT J. Morr 
Athenzum, Liverpool, Dec, 31, 1872 
Eleven-Year Rainfall Period 
THE Royal Exchange storm of Nov., 1838, happened twenty- 
two years before Prof, C. P. Smyth’s Hyperborean one of Oct., 
1860—twelve years ago. I have heard of a great one at Dantzic 
in 1816-17 (also twenty-two years before 1838). In a small 
book—‘‘ Chronological Tablets,” published 1801, article on 
“Storms,” great ones, in 1794. Oct. 6; 1784, Dec. 5; 1773, 
March; 1751, Dec. ; 1740, Nov. 1; 1703, Nov. 26 (the 
Great Storm, wide ‘‘City Remembrancer,” also Mautical 
Magazine, Jan., 1843, my extracts), this is not in the eleven- 
year series ; 1658, Sept. (death day of Oliver Cromwell, fifty- 
five years before great 1703 storm), &c. 
Now as the sun and moon are probably prime agents in these 
periodic hurricanes, we get 11 x 365} = 4017°5 days, being 
156 periods of 25d. 18h. ; 147 periods of 27d. 7h. 7m. ; and 
136 periods of 29d. 12h. 43m., nearly. 
HIN 2280S bata! very nearly. 
Hyp. log. = 1°1447300 = = 
15 I 
Offord Road, N., Dec. 16 
S. M, Dracu 
Pollen-eaters 
FRoManote in Nature, Dec. 19, it appears that it has hitherto 
been a mooted question among entomologists whether any species 
of Diptera are pollen-eaters. I have often watched certain 
slender-bodied flies, belonging to orallied to the family of Noverers 
(Syrphide), in the act of feeding on the pollen of various flowers, 
which they effected by a quick jerking and grinding movement 
of the mandibulz. I once witnessed the exhibition ofa muchmore 
surprising taste by one of these insects, which, together with a 
small yellow ant, I watched for a considerable time feasting on 
a gout of resinous matter that had exuded from a wound in the 
bark of a spruce fir-tree. 
Mention of ants reminds me of Mr. Meldola’s statement 
(Navurg, vol. vi. p. 279) that Dr. Bree has pronounced their 
aphis-milking instinct a myth. While an undergraduate at 
Cambridge, I have more than once been a pleased spectator of 
this mythical performance ; but Dr. Bree’s incredulity may be 
explained by the fact that all ants have not this instinct. At 
least, though for many years constantly on the look-out for it, 
only one instance of it has come under my notice on this side of 
the Channel. On one occasion when I introduced an ant among 
a number of aphides, her first act was to scize one of them in 
her jaws ; but after carrying it for a short distance over the 
backs of its fellows, she released it, and made what haste she 
could out of the company of creatures whose polite attentions 
she seemed by no means to appreciate. 
Kilderry, Co. Donegal W. E. Hart 
Fresh Water on the Coast of Tobago 
WITH reference to my letter of the 11th ult. (NATURE, vol. 
vii. p. 124.) I forward the following further information with 
regard to the appearance of fresh water on the coast of Tobago, 
promised from the same correspondent. 
‘“The appearance of foreign water on our southern coast in 
the months of August, September, and October, is by no means 
a rare thing. This water is always of a dark colour, emitting 
after a time a most offensive odour, and leaving on the beach a 
line of a frothy substance of a peculiar odour and yellowish 
green colour. 
**The influx to which I called your attention surpassed any- 
thing of the kind ever seen here. Iam not aware that anyone 
has tested this water, or preserved any portion of it. Mr. 
had some brought to his bath for salt water, and thinking 
that his servant had played him false, he repaired to the bay, 
(Scarborough) and found the water there fresh instead of salt, 
“*There is much difference of opinion here as to the source of 
this water. Capt. supports the views of those who hold 
that it comes from the Oronoko. To do this, that great river 
must force its food 180 miles against the equatorial stream and 
trade wind, while the rivers to windward, e.g. the Demerara, 
Essequibo, &c., discharge their water into that stream, which 
impinges on our southern and eastern shores, leaving unmistake- 
able evidence of its power. 
‘- May not the Amazon have something to do with this phe- 
nomenon? It is said to send its waters ‘pure and unmixed’ 
into the ocean 300 miles. I have had no information as to 
excessive rains on the continent.” Rawson W. Rawson 
Government House, Barbados, Dec. 2, 1872 
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