-218 
DATs 
[Dec. 23, 1869 
DEDLPERS LO LHESEDIMOR: 
[Zhe Editor does not hold himself responsible for opinions expressed 
by his Correspondents, No notice is taken of anonymous 
communications. | 
Variety and Species. 
In a recent number of Nature I noticed an extract from 
a paper read before the Literary and Philosophical Society at 
Manchester, on the subject of variety as distinguished from 
species. The author suggests the question, ‘‘ where does 
species end, variety begin?”” From experiments, he finds that 
the colours in different parts of the wings of insects treated 
with, in some cases become toned down to a more sombre 
hue, in others become mixed with the adjoining colour, and 
that they are in every case smaller. May not these differences 
be attributed to the effects of a confined and unnatural life. I my- 
self well recollect rearing a Drinker Moth when a boy at school, 
and obtaining a small, dull-coloured specimen, instead of an 
insect whose rich brown wings rival in colour those of the well- 
known “oak-egger.” But difference of colour does not consti- 
tute the only variety which is noticed in Lefidopiera, for posi- 
tion of markings and proportions of colour are equally worthy 
of notice, though not so obvious to the unaccustomed eye. 
Take, for example, the common six-spot Burnet (Zygana jili- 
pendula), of which I know three distinct forms—viz. (1), the 
ordinary one, with three clear spots; (2), having the spots all 
connected, forming an ill-defined bar of red down the centre of 
the upper wings ; (3), (a form which I believe to be in general 
very rarely met with, but of which I have myself captured 
several specimens), having the red markings of (1) supplied by 
those of a pale yellow, in both upper and under wings. Now, 
since these were all captured in one field where the three forms 
are comparatively common, may it not be more than probable 
that the difference is not to be denominated a variety, but to 
be a natural dissimilarity of form; not to be attributed to any 
physical difference of circumstances, previously to the attainment 
of the state of ‘‘imago,” but to a purely natural and unassisted 
cause? A white horse is not considered a variety because his sire 
was a bay, nor is the whiteness of a bullock considered a usws 
nature if born from tawny parents. I hope to be able to make 
experiments during the following year, which may perhaps lead 
to more conclusive results on this subject. 19) 
Cuckow’s Eggs 
I TRusT that, although some time has elapsed since Professor 
Newton’s very able paper on Cuckows’ eggs appeared in NATURE, 
I am not too late to offer a few observations on it, the more so 
as I have always taken great interest in the breeding of the 
cuckow. I cannot quite agree with Professor Newton that 
cuckows’ eggs as a rule are subject to great variety. The eggs 
of the Great Spotted Cuckow (Oaylophus glandarius) are cer- 
tainly not subject to much variety ; for in a large series from 
Africa and Spain I have found them closely resemble each other. 
Of our common cuckow (Cucelus canorius) abnormally coloured 
eggs have several times come under my observation, but I 
consider them as of very rare occurrence, and in several large 
series I have seen, but few have struck me as differing much from 
the usual type. 
Of those I possess in my own collection, the most peculiar 
variety is a large egg, the ground colour of which is a dirty 
grey, sparingly spotted and blotched with light brown, and 
somewhat resembling some varieties of the eggs of the Garden 
Warbler (Sylvia hortensis). This egg was found by the late Mr. 
E. Seidensacher, of Cilli, Styria, ina nest of the creeper (Cer- 
thia familiaris), with four eggs of the foster-parent, and was s:nt 
to prove that the cuckow must have deposited her egg with her 
bill, as the nest of the creeper was so placed that she could only 
have got her head in. A German friend of mine, residing 
near Coblentz, sent me, for inspection, last year, a most pecu- 
liar cuckow’s egg, which reminds one of that referred to by 
Salerne. This egy was rather large for that of a cuckow, and of 
a uniform bluish green colour. He did not, however, state in 
what nest it had been found. 
My own experience in field natural history leads me to con- 
firm the opinion given by Professor Newton, that the same female 
produces eggs which closely resemble each other ; but at the same 
time I have not found that the same cuckow generally makes use 
of the same species of bird as nurse for her offspring, and in this 
I am borne out by several field naturalists with whom I have 
worked. 
My friend at Coblentz wrote to me some time ago, stating that 
he had observed that the same female cuckow generally produces 
similarly coloured eggs, and that he had found in a nest of 
Turdus merula a peculiar and abnormally coloured egg of the 
common cuckow, closely resembling that of the common bunting 
(Emberiza miliavia), and shortly after found in a nest of the 
Robin (SyZvia xubecila), situated close to the blackbird’s nest 
above referred to, another similar cuckow’s egg. He further 
states that the cuckow is not a common bird there, and that he 
had good reasons for supposing that the two eggs were produced 
by the saine female ; also that in 1867 the same thing occurred, 
when he found peculiarly coloured cuckows’ eggs in nests of the 
Chiffchaff and Willow-wren. 3 
As far as my own experience goes, I cannot testify to the 
correctness of Dr. Baldamus’s theory, as amongst all the cuckows’ 
eggs I have collected, I find scarcely any that resemble those of 
the foster-parents. JI have now before me eggs of our common 
cuckow taken with the following species, the eggs of which I 
have with each cuckow’s egg, viz.: Sy/via arundinacea, S. rube- 
cula, Certhia familiaris, Emberiza hortulana, Sylvia palustris, 
S. cinerea, Motacilla alba, and Accentor modularis, none of 
which, excepting that found with the eggs of Sy/uia cinerea, bear 
any resemblance to the eggs of the foster-parent. The eggs of 
the American cow bunting (JZolo‘hrus pecoris) which, like our 
cuckow, entrusts its offspring to foster-parents, seldom, I believe, 
resemble those of the foster-parent, and in the instances that have 
come under my own observation I have found them to differ 
very widely from the foster-parent’s eggs. On the other hand, 
the eggs of the Great Spotted Cuckow (Oxylophus glandarius) 
are so strikingly similar to those of the common Magpie, in whose 
nests they are generally placed, that it is often difficult to dis- 
tinguish them except by handling them, the texture of the shell 
being very different from that of the magpie’s egg. In Spain 
they are, howeyer, occasionally found in the nests of the Azure- 
winged Magpie (Cyanopica Cookii,) from the eggs of which bird 
they differ very much. H. E. DRESSER 
Physical Meteorology 
In Mr, Balfour Stewart’s suggestions (NATURE, p. 192) he 
refers, as an illustration of his method, to a frequently falling 
barometer in the centre of a cyclone while air is rushing in from 
every side, and asks, ‘‘ What can carry off the air if there be 
not an ascending current in the very heat of the cyclone?” I 
would therefore ask his consideration of the grounds on which, 
as I believe, such an ‘‘ascending current” mst there take place 
on the simple principle that great heat has been evolved. 
It is well known—(1) That long-continued and heavy rainfall 
takes place in any area of low pressure with higher pressure out- 
side of it. (2) That the greater part of the rain which falls, 
during storms, descends in the front part of the atmospheric 
depression which attends the storm; and (3) That the rainfall 
is proportional to the suddenness and extent of the fall of the 
barometer. Now, though mere segwence does not prove a 
connection as ‘*Cause and Effect,’ it certainly saggests it 
if the supposed cause be adequate to produce the effect. Let B 
represent a certain weight, the latent heat of vapour at (10° Cent.) 
50° Fahr. is (Regnault 599°.5 Cent.)=1079° Fahr. But specific 
heat of air is to that of water as 0.2375 : 1 (Regnault). Conse- 
quently B of yapour condensed would heat B of air (x 
4543. of Fahr. 
When a warm and very moist equatorial current meets and 
intermingles with a cold polar current (from the known laws of 
vapour) the column of air, thus mixed, must deposit a certain 
amount of moisture. Let us assume the mixed stream to be 
about 1,000 feet in thickness, and that 34; of an inch of rain 
falls suddenly on the surface. 1,000 cubic inches of air weigh 
about 310 grains, and ;45 cubic inch of water about 25} grains. 
Consequently, the latent heat of this 5 inch of rain would heat 
S54 23}) 370° of Fahr. which 
must occasion an enormous ascending current of air, thereby 
producing a sudden diminution of the pressure at the surface, 
and causing a large influx of air to restore the equilibrium. 
We know that ‘‘whirlwinds” arise from ‘‘local heating” (as 
in dust-storms or prairie-fires) ; hence a like effect must result 
from such local evolution of heat through the condensation of 
atmospheric vapour, and the heated column of air will ascend 
(as a whirlwind in the upper strata) de/ore the like effects are 
the air of the 1,000 feet column ( 
