508 
NATURE 
[March 17, 1870 
the imaginary two-foot rule—and why is about 115 feet more 
common than other distances? 
I think it probable the sort of objects with which a man is 
familiar in his daily life may have some influence on his judg- 
ment in this respect. The men I questioned were for the most 
part engaged in warehouse or out-door work. I should like to 
know what answers watchmakers or jewellers would give. 
This theory, however, fails to account for the different estimate 
formed by the same individual when the moon is high above, or 
on the horizon ; but I imagine, in the latter case, the imaginary 
rule is superseded, or more properly modified, by the terrestrial 
objects which are in the field of vision with the moon. 
Cardiff, March 7 GEORGE C. THOMPSON 
Cuckows’ Eggs 
May I be permitted to make a few observations upon Mr. 
Sterland’s letter in your issue of the 27th of January, relative to 
the cuckows’ eggs’ controversy. 
In answer to Prof. Newton’s query, ‘‘If the eggs in question 
were not cuckows’, what birds laid them?” Mr. Sterland says, 
“« My reply is simply that they were laid by the birds in whose 
nests they were found.” 
Besides the well-known fact mentioned by Mr. Newton 
(NATURE, p. 266), “that when birds lay larger eggs than usual 
the colouring is commonly less deep,” which tells so strongly 
against Mr. Sterland, I will only mention the following 
instances. 
st. The egg No. 9 in the series given by Herr Baldamus, 
(see Zoologist for April 1868), which the Royal Forester, Mr. 
Braune, found 77 the ovary of a just-killed cuckow, and which 
**was coloured exactly like the eggs of Hypolais.” 
andly. The egg No. 26 in the same series, belonging to the 
collection of Dr. Dehne, described as a “light-greenish blue egg 
without any markings,” and ‘‘ might have passed for the egg of 
either species of the redstarts,” which specimen ‘‘was /atd iz a 
cage bya cuckoo that was caught in a hay loft.” (The 7ta/ics 
are mine.) 
3rdly. The two instances given by Mr. H. E. Dresser, 
(NATURE, p. 218) of two eggs of the cuckow ‘‘ closely resem- 
bling” those ‘* of the common bunting (Zderiza miliavia),” one 
found in a blackbird’s, the other in a robin’s nest. 
Can Mr. Sterland explain away the Ist and 2nd instances ? 
and how does he reconcile the 3rd instance with his affirmation ? 
Will he venture to say that the two apparent bunting’s eggs were 
laid by a blackbird and a robin respectively, or, will he risk 
the remark that a common bunting had taken a cuckow-like 
freak into its head and been laying its eggs in other birds’ nests ? 
As either alternative is too absurd to be worth a moment’s con- 
sideration, we can only conclude that they are cuckows’ eggs, 
unless there has been some mistake as to the nests from which 
they were taken—scarcely likely, if Mr. Dresser’s remarks are 
carefully read. 
Therefore I think Mr. Sterland must admit, if he accepts 
these facts as authentic, that the cuckow’s eggs do vary to a large 
extent, and doing so, he has little foundation for doubting the 
identity of the specimens mentioned by Herr Baldamus as taken 
from nests whose eggs they resembled. 
For my own part I have every confidence in the discrimina- 
tion of that ornithologist, and am not afraid that he had been 
carried away by a pet theory that led him to zagine this or that 
egg taken ‘out of the nest of the hedge-sparrow or tree-pipit ” 
to be a cuckow’s merely because itis ‘‘an egg rather larger than 
the rest, but marked and coloured in a similar manner.” If Mr. 
Sterland will carefully examine Herr Baldamus’s evidence he 
will find that it is not of such a superficial character. 
I agree with Mr. Sterland that it is certainly singular that 
British and Continental observers should come to such opposite 
conclusions as to this variation of the cuckow’s egg in their re- 
spective countries ; but this is no reason for impeaching (merely 
because our experience differs) the testimony of the eminent Con- 
tinental oologists who affirm this extreme variation, and to some 
of whom Herr Baldamus’s theory is probably unknown; as in- 
stance, in the two quotations by Prof. Newton (NATURE, p. 266) 
from Des Mfrs and Degland et Gerbe. 
Can it be that such extreme variation really does occur on the 
Continent, and is yet comparatively absent in Britain? I leaye it 
to abler hands than mine to discuss ; but if it should prove so, it 
will be another feature in the already remarkable habits of the 
cuckow. 
Tadcaster, Feb. 7. Francis G, BINNIE 
MR. RUSKIN ON RIVER CONSERVATION 
N his recent Friday evening discourse on Verona and 
its Rivers, at the Royal Institution, Mr. Ruskin, 
speaking of the Adige and the Po, said: “I want to 
speak for a minute or two about these great rivers; be- 
cause in the efforts that are now being made to restore 
some of its commerce to Venice precisely the same ques- 
tions are in course of debate which again and again, ever 
since Venice was a city, have put her Senate at pause— 
namely, how to hold in check the continually advancing 
morass formed by the silt brought down by the Alpine 
rivers. Is it not strange that for at least six hundred 
years the Venetians have been contending with those 
rivers at their 7ou¢is—that is to say, where their strength 
has become wholly irresistible—and never once thought 
of contending with them at their sources, where their 
infinitely separated streamlets might be, and are meant 
by Heaven to be, ruled as easily as children? And ob- 
serve how sternly, how constantly the place where they 
are to be governed is marked by the mischief done by 
their liberty. Consider what the advance of the delta of 
the Po in the Adriatic signifies among the Alps. The 
evil of the delta itself, however great, is as nothing in 
comparison of that which is in its origin. The gradual 
destruction of the harbourage of Venice, the endless cost 
of delaying it, the malaria of the whole coast down to 
Ravenna, nay, the raising of the bed of the Po, to the im- 
perilling of all Lombardy, are but secondary evils. Every 
acre of that increasing delta means ¢he devastation of 
part of an Alpine valley, and the loss af so much fruit- 
Sul soil and ministering rain. Some of you now present 
must have passed this year through the valleys of the 
Torcia and Ticino. You know, therefore, the devastation 
that was caused there, as weil as in the valley of the 
Rhone, by the great floods of 1868, and that ten years of 
labour, even if the peasantry had still the heart for labour, 
cannot redeem those districts into fertility. What you 
have there seen on a vast scale, takes place to a certain 
extent during every summer thunderstorm, and from the 
ruin of some portion of fruitful land the dust descends to 
increase the marshes of the Po. But observe further— 
whether fed by sudden melting of snow or by storm— 
every destructive rise of the Italian rivers signifies the loss 
of so much power of irrigation on the south side of the 
Alps. You must all well know the look of their chain— 
seen from Milan or Turin late in summer—how little snow 
is left, except on Monte Rosa, how vast a territory of 
brown mountain-side heated and barren, without rocks, 
yet without forest. There is in that brown-purple zone, 
and along the flanks of every valley that divides it, an- 
other Lombardy of cultivable land; and every drift of 
rain that swells the mountain torrents, if it were caught 
where it falls, is literally rain of gold. We seek gold 
beneath the rocks; and we will not so much as make a 
trench along the hillside to catch it where it falls from 
heaven, and where, if not so caught, it changes into a 
frantic monster, first ravaging hamlet, hill, and plain, 
then sinking along the shores of Venice into poisoned 
sleep. Think what that belt of the Alps might be—up to 
four thousand feet above the plain—if the system of 
terraced irrigation, which even half-savage nations dis- 
covered and practised long ago in China and in Borneo,and 
by which our own engineers have subdued vast districts 
of farthest India, were but in part also practised here— 
here, in the oldest and proudest centre of European arts, 
where Leonardo da Vinci—master amongst masters—first 
discerned the laws of the coiling clouds and wandering 
streams, so that to this day his engineering remains un- 
bettered by modern science: and yet in this centre of all 
human achievements of genius no thought has been taken 
to receive with sacred art these great gifts of quiet snow 
and flying rain. Think, I repeat, what that south slope 
