228 
NATURE 
| Fan. 19, 1871 

The gist of his argument lies in his assertion, that “if a true 
pound, as determined at London, were carried to the North 
Pole, it would weigh more than a pound.” 
Now, since the determination of a pound is actually effected 
by making it a copy of a standard so that they shall counterpoise 
each other 77 vacuo, it is strictly independent of locality. 
The standards actually employed for this purpose, for example, 
the authorised copies of the principal standard pound which 
have been sent to various countries, have been made as nearly 
identical in mass as skilled workmen could make them, and have 
been sent at random to different latitudes. 
Similar remarks apply to the weights in a chemist’s box. 
Surely it is not seriously proposed that the chemist should file 
them down to accommodate them to the increase of grayity, 
when he takes them from London to Edinburgh. 
Where should we find ourselves, if the makers of chemists’ 
weights endeavoured to make them of different masses, accord- 
ing to the places where they were to be used ? 
Fortunately, this has never been attempted ; and since all 
parts of the world are in possession of practically identical 
standards of mass, under the name of standard pound or standard 
kilogramme, and tolerably accurate copies of these and their 
fractional parts are in everybody’s hands, why not acknowledge 
them as standards of mass, which they are in point of fact, 
although, according to the theory which I am combating, they 
ought not to be? 
Those who hold that theory must choose between two evils :— 
they must either make the pound a unit of force, in which case 
they must file or load their weights as they go from place to place 
(this seems to be the alternative which W M. W. chooses) ; or 
they must accept the gravitating forces of equal pieces of metal 
as nominal units of force at the different localities where these 
pieces of metal may happen to be, although these forces are 
really not equal. This latter alternative, which gives a variable 
unit of force, has been commonly adopted till recently, and a 
variable unit of mass has been conjured up to suit it, 
If our spring-balances were as accurate as our standard 
weights, W. M. W.’s idea would be practicable. The equality 
of two forces at different places could then be very directly 
tested; but, in fact, the mostaccurate means we possess of making 
such a comparison consists in a double process, a weighing with 
the ordinary balance, combined with a difficult and less accurate 
pendulum-comparison. Inasmuch then as ease and accuracy of 
comparison is the first essential of a scientific standard, I submit 
that the world is right in employing standard pounds of equal 
mass and not standard pounds of equal gravitating force. 
Much confusion arises from using the word wetg/¢ in a con- 
nection which leaves it doubtful whether sass or gravitating force 
is meant. I trust you will keep your columns open for the 
further discussion of this question, as it much needs ventilation. 
Belfast, January 11 J. D. EveREeTT 

The Tails of Comets, the Solar Corona, and the Aurora 
considered as Electric Phenomena 
In reference toa letter from Mr. Bedford, Ph.D., published 
in your last number, allow me to state— 
I. That I had never seen or heard of Dr. Bedford’s theories. 
2, That, judging from the extract given in his letter, Dr. 
Bedford has not published anything analogous to the electrical 
hypothesis which I have put forward. In his letter he has 
misquoted and made omissions to the extent of one-half the 
heading, in order, I suppose, to avoid the very mention of the 
word electricity, which, on the other hand, is the very substance 
of my postulate. OSBORNE REYNOLDS 
Owens College, Jan. 17 
Apparent Size of the Moon 
From almost any place in the balcony of St. James’s Hall, at 
an evening performance, one may find in the coronets of gas- 
jets, forming one or more of the arches across the roof, cor- 
roboration of what I wrotein NATURE of May 12, 1870 (vol. ii. 
p- 27). The nearest or first coronet, and the two next, observe 
a gradation of increase in apparent magnitude, as they should 
do. But the rest, which (unlike those three) descend towards 
the horizon, and should, nevertheless, observe a gradation of 
increase, are apparently all of a size. I call attention to this 
“* unconsidered trifle ” as having the full force of a very elaborate 
experiment. C. M. INGLEBY 
Ilford, Jan. 7. : 

Atmospheric Currents 
THE following is part of a letter signed ‘G.” in NATURE of 
6th October, 1870 :— 
“It is very important to obtain correct and copious data 
regarding the atmospheric currents between say 5,000 feet and 
five miles above the level of the sea, and especially at various 
points on and near the equator, and at about 30° to 32° North 
and South latitudes. Within these limits the rain-bearing 
currents of the atmosphere move. If self-registering meteoro- 
logical instruments were placed permanently upon several of the 
| leading mountain ranges of the world, and their records copied 
at stated intervals, we should obtain valuable data for determining 
the direction, velocity, and magnitude of the controlling atmo- 
| spheric currents of the globe.” 
This suggestion is most valuable, but it would involve a 
source of error that would be difficult to allow for. Most 
mountain ranges occupy so extensive an area that they have 
their own local climates, and indications on such ranges would 
consequently not give accurate information about the currents 
where they are not modified by such influences. The most 
valuable information will be obtained from the most isolated 
mountains. The most isolated mountains of sufficient height, 
within sufficiently easy reach of us, are Etna and Teneriffe. 
Etna is in the variables, and Teneriffe in the trade-winds. 
I do not, however, agree with the following suggestion, that 
more valuable observations still might be obtained by means of 
captive balloons. Balloons cannot be used in stormy weather, 
and they are also subject to the great disadvantage, that they tell 
nothing about barometric fluctuations : because the height of a 
balloon above the earth can be known only from the barometer, 
and consequently there is no way of ascertaining the indications 
of the barometer at a known height. It is not at all certain that 
the barometric curves at the summit and at the base of Etna or 
Teneriffe would present any close correspondence. Sets of 
barometrical and other meteorological observations taken for 
sufficiently long periods at the summit and at the base of such 
mountains would be probably the most valuable of all data for 
meteorological science in its present state. 
JosrrH JOHN MURPHY 
Old Forge, Dunmurry, Co. Antrim, Jan. 14 


THE AMERICAN ECLIPSE EXPEDITION 
eee portion of the American Eclipse Expedition 
which was stationed at Xeres was favoured by 
weather which enabled the observers to examine the 
Corona during the whole period of totality, and with some 
results of interest ; an informal account of a part of which 
the kindness of Professor Winlock enables me to lay 
before your readers. 
The party was in charge of Professor J. Winlock, and 
stationed in an olive grove about a mile from the city, the 
property of Mr. Davies, of Xeres, to whom all the members 
of the expedition are indebted for continual aid and 
kindness. The observations for the determination of 
longitude, latitude, and times of contact were conducted 
by Assistant G, W. Dean, of the Coast Survey, aided by 
Captain Ernst, of the U.S. Engineers, and by Mr. 
Gannett, of the Harvard College Observatory. 
Their labours were facilitated by the courtesy of the 
Director of the neighbouring Observatory of San Fernando, 
with which telegraph connection was established, and the 
results attained will be found in full in their official report. 
Besides the instruments of precision, the party was pro- 
vided with four equatorial telescopes of from six to eight 
inches aperture, driven by clockwork, and many smaller 
ones. One of the largest telescopes carried an objective 
specially corrected for actinic rays, with which, and a 
companion instrument, photographs were taken during the 
totality and previous stages by Mr. Willardand his assistant. 
In addition, a photographic telescope of upwards of 
thirty feet focus, placed horizontally, and receiving the solar 
rays from a heliostat, was used, in charge of Mr, Gannett. 
The accessories of the instruments were such as the 
previous experience of the observers (nearly all of whom 
had witnessed the eclipse of August 1869) suggested, and 
were too numerous for description here, though a means 
