448 
NATURE 
‘| April 6, 1871 | 


it burst into flame ; very soon the mass melted and rose to an 
intense, white heat, the air streaming in through the spiral greatly 
favouring the combustion, a full spectrum of the utmost purity 
and splendour was formed, which continued as long as the white 
heat lasted, but afterwards declined from, and rapidly at, the 
violet end through the whole spectrum to the red, which per- 
sisted longest. On repeating the experiments, and raising a very 
narrow slit to the spectroscope, I found, as I anticipated, the 
sodium line reversed, and I had before me a miniature sun, a 
glowing centre emitting light of every wave-length, while 
the melted sodium, flowing through the intervals between the 
wires of the lower part of the cone and being dissipated by the 
heat, surrounded the liquid centre with an atmosphere absorbing 
light of its own refrangibility. 
Thinking some of your readers would like to repeat so simple 
and inexpensive an experiment, I have ventured to send you 
this. . 
St. Mary Church, Torquay 

A Wind-direction Rain-gauge 
In your issue for yesterday, March 30, at page 433, you give 
a paragraph respecting a ‘* Wind-direction Rain-gauge.” Might 
I be allowed to observe that a gauge on the same principle has 
been in use at this place for many years, ‘‘ it is arranged for four 
vessels” only, showing N. to E., E. to S., S. to W., and W. 
to N. Wm. LYALL 
Literary and Philosophical Society, Newcastle-upon-Tyne 
Entomological Queries 
CAN any of your entomological readers refer me to any works 
or memoirs on British Ants published since the appearance of 
Westwood’s “ Classification of Insects,” and not quoted by Mr. 
Smith in his volume on ‘“‘ Formicidze ” in the British Museum 
Catalogue? What is the scientific name of the Texas agricul- 
tural ant and of the smaller ant which it ejects from its colonies ? 
And where can I find M. Lespes’ paper or papers on the 
“Domestic Economy of Formicaries,” especially with regard to 
the Clavigers and other blind beetles ? A, EMMET 
Feb. 21 
Rain produced by Fires 
In your No. of Feb. 16, there is a letter from Mr, Laughton on 
the Artificial Production of Rains, which is worthy of notice 
from a strictly scientific point of view. I have little doubt that 
rains have been in comparatively rare cases caused by large fires. 
We may dismiss from our minds the idea that rains can be pro- 
duced, even when the conditions are favourable, by all the 
powder that is burnt during a battle on land or sea. It is said 
that ‘‘in a problem of this nature, negative examples have more 
weight than positive.” But it is surely more philosophical to 
hold that the one class of instances is as valuable as the other. 
If rains have sometimes been produced by fires, it is as well to 
try to eliminate the conditions under which they occur as in those 
cases in which they do not occur. 
It is curious enough that much of the popular belief as well as a 
disbelief in the connection between rains and fires must be 
ascribed to the late Prof. Espy. After laying down with scientific 
accuracy the atmospheric conditions for such an occurrence, he 
somewhat lost sight of the principles in his instructions to the 
farmers of the United States for burning their felled timber for 
the production of rain. I need not enter into these. The 
negative cases are found to be numerous enough. Great fires 
rage over the Prairies and through the woods in America for 
weeks during the autumn, and the air becomes darkened by a 
veil of smoke, while no clouds are to be seen. This usually 
occurs when the wind is from the west and the air dry, and 
naturally blue and bright till obscured by smoke. In such in- 
stances the theory of fires producing rains justly enough becomes 
unpopular. 
On the other hand Espy laid down with great precision the 
conditions under which rains will result from great firesin ‘‘a high 
dew-point and a calm atmosphere.” In short, the air must be 
pretty well saturated with moisture, and verging upon that un- 
stable state of equilibrium under which cumulus clouds are 
formed. As Espy has shown, and every observer of the 
phenomena will confirm, the gorgeous cumulus clouds of 
summer are not seen when the air is much disturbed by winds. 



Their very formation and existence depend upon ascending cur- 
rents. Previous to Espy’s investigations, it was supposed that 
the formation of cumulus was due to the expansion of the vapour 
of water by the heat of the sun and its consequent diffusion up- 
wards through the permanent gases till it was condensed above. 
He clearly showed by experiment that vapour has little power of 
permeating air under the ordinary pressure of the atmosphere. 
And he drew the inference that it could be only carried into the 
higher strata by ascending currents. This, 1 think, is amply 
borne out in the formation of all clouds. 
Fires then, are only likely to produce rains during comparatively 
calm weather. In the positive instances given by Espy, most 
of the observers state that the air was calm and sultry. One of 
the staff of the United States surveyors when in Florida men- 
tions, that by fuing the bush ‘‘ whenever there was no wind 
stirring, we were sure to get a shower.” Great fires are con.- 
paratively rare in this country, and I have never seen the forma- 
tion even of cloud here 1rom such a cause. However, I did 
once observe this phenomenon. Many years ago when sailing 
up the Mississippi near its mouth, in a clear and cool evening, 
after the subsiding of a “Norther,” a great fire was burning 
among the reeds on its west bank. Above the dark smoke the 
true cumulus cloud was distinctly formed. Its bright and rounded 
form was beautifully brought out in the setting sun. No other 
clouds were visible around, and these were soon left behind as 
we ascended the river. 
If we reflect on the matter it is difficult to conceive how clouds 
could be formed by means of fires during windy weather. The 
ascending columns could not be formed under such conditions, 
for the heated air would be rapidly swept off, and diluted with 
the mass of air rushing past. This may be illustrated by other 
examples better known than the formation of the cumulus. 
Volcanoes are well known to produce at times clouds as well as 
rains. But all the vapour or heat that Vesuvius could emit 
during an active eruption wouldnot produce rains when a strong 
and dry north-west wind was blowing across its top. So also 
the beautiful and true cumulus cloud that so often hovers over the 
Falls of Niagara is only seen in calm weather. Under favour- 
able atmospheric conditions I have lately been informed by Dr. 
Henry Washington that the Niagara cloud sometimes gives rise 
to rains and electrical phenomena. The true inference seems to 
be that great fires will not produce rain, excepting “the air is 
calm, and the dew-point high,” RosBert RUssELL 
Pilmuir, Leven, Fifeshire, 


A BILL TO ESTABLISH THE METRIC 
SYSTEM OF WEIGHTS AND MEASURES 
THE following Bill, prepared and brought in by Mr. J. B. 
Smith, Sir Charles Adderley, Sir Thomas Bazley, Mr, 
Graves, Mr. Baines, Mr. Albert Pell, Mr. Muntz, and Mr. 
Dalglish, has been ordered to be printed by the House of 
Commons :— 
Whereas it is desirable that the weights and measures of the 
United Kingdom should be decimalised, and made to correspond 
with those of other countries. 
And whereas the use of metric weights and measures is now 
legal, but no provision has been made for procuring the standards 
of said metric weights and measures, and for verifying and 
stamping those in use under the said Act. 
Be it enacted by the Queen’s most excellent Majesty, by and 
with the advice and consent of the Lords Spiritual and Temporal, 
and Commons in this present Parliament assembled, and by the 
authority of the same as follows :— 
1. From and after the expiration of ( ) years after the 
passing of this Act, the length of the metre to be prepared 
under the authority of the Privy Council for Trade, verified by 
comparison with the original standard in Paris, having the words 
and figures ‘‘Standard Metre, 1871,” engraved upon it, and 
kept in the custody of the Warden of the Standards, shall he 
and is hereby declared to be the unit or only standard measure 
of lineal extension, wherefrom or whereby all other measures of 
extension whatsoever, whether the same be lineal, superficial or 
of capacity, shall be derived, computed, and ascertained, and all 
such measures shall be taken in decimal multiples or decimal 
parts of their respective units. 
2. The unit of the measure of surface shall be the square of 
ten metres, which shall be and is hereby denominated the ‘‘ are.” 
