Feb. 16, 1871 | 


theme amongst popular meteorologists ; but in regard to this also 
there isthe same uncertainty. Several battles and bombardments 
have been followed by storms ; but, on the other hand, several 
have not. The general opinion amongst naval men is that 
heavy firing beats down the wind and produces a calm ; and it 
is tolerably certain that this is frequently the case, more espe- 
cially if the wind is light. Whether it does or not, the sudden 
irruption of millions of cubic feet of gas into the lowest strata 
of the atmosphere and within a very limited area, must have a 
tendency to cause disturbance, a tendency increased by the 
undulatory movement due to the noise of the guns. The battle 
of Trafalgar (October 21st) was fought in a very light westerly 
breeze, which, towards the afternoon, almost entirely died away. 
During the night the wina gradually freshened, and by noon 
the next day blew very hard. - Lord Collingwood in his despatch, 
dated the 22nd, says it had “blown a gale of wind ever since 
the action ;” but that this is merely a general way of speaking 
is seen by a reference to the logs of the various ships of the 
fleet. (Despatches of Lord Nelson, vol. vii., pp. 159, e¢ seg.) 
A westerly gale, on the coast of Portugal or Spain, is not such 
an unusual occurrence in the end of October, as to compel us to 
attribute one to a battle which took place twenty hours before 
it came on. Again, the battle of St. Vincent, of the Nile, 
Rodney’s action off St. Domingo, and many others, do not seem 
to have been followed by any interruption to the usual fine 
weather. Quatre-bras was followed by heavy rain; but the 
night after Waterloo was fine, and the bright moonlight is 
specially mentioned as advantageous to the pursuers ; and though 
Mr, Belcher speaks of rain as having set in in the east of France 
during the present campaign, I have not seen any notice of its 
following the battles of Gravelotte or Sedan, so as to be clearly 
referable to them. 
What appears to me the only explanation of the apparent 
contradictions in the evidence is this ; that large fires, explosions, 
battles, and earthquakes, do tend to cause atmospheric disturbance, 
and especially, to induce a fall of rain ; but that for the tendency to 
produce effect, it is necessary that other conditions should be 
suitable ; that rain does not follow, unless the lower air contain 
a great deal of moisture; and that therefore the ascensional 
movement does not reach toa height such as we might at first 
be led to conceive ; that, in fact, the height is for the most part 
very trifling. With regard to storms said to have been caused 
by some of these agencies, the evidence is still more un- 
satisfactory ; and, in our present ignorance of the cause of storms 
generally, is quite insufficient to compel us to attribute any one 
particular gale, extending probably over a wide area, to some 
very limited and comparatively insignificant disturbance. 
; J. K. LaucHtTon 

Natural Science at Cambridge 
THE rejoinder in your last number (p. 287) to my inquiries is 
rather ingenious than ingenuous. ‘‘ The Writer of the Article 
in Question” vouchsafes no answer to my very plain questions 
(p. 264), but is kind enough, instead of justifying his own state- 
ment, to propound sundry suggestions, surmises, and what not. 
I simply asked for confirmation of a certain assertion. This he 
avoids giving, and, though I regret the cause, I do not wonder 
at it. Some persons may think it would have been better taste 
to have acknowledged that the assertion was unfounded. Perhaps 
your correspondent is of another opinion ; if so, I do not wish 
to interfere with him. I have only to remark that substantially 
he admits the force of the doubt I expressed by now modifying 
his previous statement as to ‘‘most of the colleges ” into ‘* some 
colleges ”—perhaps ‘‘ one college” would have been nearer the 
mark, but I will let that pass, hoping that when he again writes 
on the subject, events may have proved him to be a true prophet. 
Cambridge, Feb. 10 

Glass Globes 
In consequence of the letter of Col. Greenwood, which ap- 
_ peared in NATURE of the Ist December last (No. 57, p. 87), I 
wrote to Dr. G. O. Sars, of Christiania, who is the Inspector of 
Sea-fisheries in Norway, for information on the subject. In his 
reply, just received, he says he was not aware that such globes 
were used as net floats in any other country than Norway, and 
that until quite recently they had been used there in the great cod 
fisheries at Lofoten only. At Séndmér, in Christiansand, they 
had begun to come into use in 1869, but by no means generally 
NATURE 



307 
He has no doubt that the floats washed ashore in Shetland and 
the Hebrides came from Lofoten ; but he remarks that their 
course in a south-westerly direction is quite contrary to what 
might be expected from the action of the equatorial current ; and 
he suggests that before reaching our northern coasts the floats 
made a very long course, having been first carried northwards 
until they got within the range of the Polar stream, by which 
they may have been carried southwards along the coast of Green- 
land, and so at last coming within the influence of the Gulf- 
stream, they were carried eastward across the Atlantic, and thence 
drifted by south-westerly winds to their destination. He adds 
that the fact of their having been found on the west coast of the 
Isle of Lewis seems to confirm this hypothesis. 
Feb. 13 J. Gwyn JEFFREYS 
P.S. on another subject. The correspondents in recent num- 
bers of NATURE do not appear to have been aware of Dr. Car- 
penter’s and my remarks in the Atheneum of the 22nd of 
October last on the hypothesis of the Cretaceous formation being 
continued or not continued up the present time. 

The Primary Colours 
Here is another proof that violet is the third primary. Prof. 
Tyndall, with that sagacity which results from the right use of 
his imagination, has given us a reason for the blue colour of the 
sky. It is probably the true reason, and it proves that blue is 
not a primary colour. The smallest light-waves are those of the 
extreme violet. These, therefore, are the waves which will be 
reflected in greatest proportion by the minute particles of foreign 
matter in the air. Why is not the sky violet then, instead of 
blue? Plainly, because although violet predominates in the re- 
flected light, there is also asmall proportion of green and a still 
smaller proportion of red. Suppose the ratios to be 1 red, 3 
green, 6 violet, and suppose the ratios for white light to be r red, 
2 green, 4 violet, Then, the light of the sky will be white Als 
I green, 2 violet, which is blue. In Professor Tyndall’s experi- 
ment on the decomposition of sulphurous acid gas by a beam 
from the electric lamp, he tells us that, as the particles of the 
sulphur cloud grow larger, the colour changes from pale blue to 
deeper blue, and then to whitish blue and white. 
No colour but blue makes its appearance, because there is 
always some green and red, as well as violet ; and always a sur- 
plus of green over red, more than enough for white light. 
Leicester, Jan. 28 FREDERICK T. Morr 

Yellow 
Ir would seem to me that the great difficulty of conceiving 
yellow as a compound colour is the brightness or lightness of 
yellow, as compared with its components. In the spectrum, we 
have the maximum of light in the yellow, and it is against our 
experience to put two dark colours together and form one light 
one, as, for example, to put the red and green together and form 
yellow. But there is just the same difficulty in the production of 
white light from all the colours of the spectrum, for we regard 
white as lighter than any of the colours, even than yellow. This, 
however, is a mental fallacy, and if once exposed, seems to me 
to do away with the difficulty of conceiving white as made up of 
a series of colours. Our ideas of colours and tints are derived 
from our own experience, and we produce tints by pre- 
cisely the opposite method to that of nature. Nature’s method 
of painting a blade of grass is, to throw on it all the colours 
of the spectrum, and afterwards pick out those which shall have 
a restdue of green. The artist’s method is to see what colours 
will produce green and then lay those on. I do not think it too 
much to say that all colours are merely tints of white—that, for 
example, yellow is really yellowish white, green, greenish white, 
and so on. If we taketwo cards, one green, the other red, and 
hold them so that the light is properly reflected from the one on 
to the other, the cards do not appear black but white. If the 
red and green were pure colours, the cards should of course 
appear black, for the light from the green card would be totally 
absorbed by the red card, and similarly with the red card. The 
white cannot be produced by a combination of the red and green, 
but by the extinction on one card of the green that gives the 
greenish white, and on the other of the red which gives the 
reddish white. That yellow is but little different from white is 
well illustrated in the beautiful experiment of Newton’s of syn- 
