Fan. 26, 1882] 
NATURE 
291 
ture corresponding to the absolute temperature. The thermo- 
electric position of iridium among seven other metals for tem- 
perature-differences 0° and 98°°6 is thus indicated— 
— Al, Su, In, Zn, Ag, Au, Cu, Fe + 
with smaller differences (0° and 5° or 10°) it comes after Au Zn. 
Once more, elements were constituted of indium in its chloride 
with zinc, copper, and iron in their chlorides, and examined. 
In the element indium-zinc, the indium is the positive pole ; in 
the two others the negative. The electromotive force of In/Zn 
was found equal to 0°331 Daniell ; of Fe/In = 0°160 D., and of 
Cu/In = 07584 D. 
IN a paper communicated to the American Association for the 
Advancement of Science Dr, E. L. Nichols discusses the relation 
between the electric resistance of platinum and its coefficient of 
expansion by heat. He has made careful experiments by an 
ingenious method at temperatures rising up to 3000” C., and finds 
that all the empirical formule given previously by Siemens, 
Matthiesen, and Benoit are unreliable, and, from certain anomalies 
in the behaviour of the metal he concludes that it is safer to 
infer the temperature from its expansion than from its electric 
resistance. 
TORNADOES, WHIRLWINDS, WATERSPOUTS, 
AND HAILSTORMS? 
iis 
[ee Dust Storm of India and other dry, hot climates, 
is another well-marked type of the whirlwind. The 
observations and illustrations of these meteors, which 
have been made by Baddeley and others, are in a high 
degree instructive from the light they throw on the actual 
movements of the whirlwind which the dust-laden air- 
currents of the storm present in a visible form to the eye. 
Previous to the outbreak of a dust storm, the atmosphere 
is unusually calm and sultry, thus essentially resembling 
the conditions of weather under which the tornado and 
whirlwind originate and which point to a vertical disturb- 
ance in the equilibrium of the atmosphere. The simplest 
form of the dust storm is that of a tall aérial column of 
sand moving onwards, and drawing into itself as it whirls 
round in its course, dust and other light bodies within the 
sweep of the strong air-currents which blow along the 
surface and converge vorticosely round the base of the 
column. A frequent form is shown in Fig. 4, which re- 
presents several dust columns grouped together, each 
whirling independently round its own axis with incurving 
air-currents at the base, whilst the group is bodily borne 
forward, presenting remarkably striking aspects as the 
forms and relative positions of the columns are changed. 
While engaged early in 1851 in the investigation of dust 
storms, Dr. Baddeley followed one on horseback, and was 
fortunate to note several of the important phenomena of 
these storms. As the dust storm passed various objects 
in its course, such as tents, horses, &c., it gradually 
diminished in size, till instead of a whirling circle of five 
or six feet in diameter, composed of several rotating 
eddies, or spirals of dust, such as are seen in Fig. 4, it 
terminated in a single cone, the apex of which in contact 
with the ground, rotated briskly from left to right, just as 
the whirling composite circle had done. From the cone 
of dust, a long ribbon-like band about a foot across, of 
equal dimensions throughout, extended into the atmo- 
sphere as far -as the eye could see, but as its sides pre- 
sented a greater opacity than the central portion it was 
really of a cylindrical form. This column was rendered 
visible by the dust it had whirled aloft, and was further 
observed to exhibit by the light of the sun which shone 
through it, a kind of vermicular spiral motion. Aloft the 
column extended forwards in advance of the whirling 
cone. Suddenly the lower portion of the column which 
continued to rotate to the last vanished, and the upper 
portion then slowly receded upwards and onwards till it 
passed out of sight. 
The important character of the evidence adduced by 
* Continued from p. 157. 
the observations of dust storms towards a correct under- 
standing of the whirlwind consists in the circumstance 
that it affords conclusive evidence that there is a strong 
inflow of the air along the surface of the ground all round 
vorticosely towards the base of the whirlwind, and that 
these same inflowing air-currents thereafter ascend 
through the air along the centre of the whirlwind, carrying 
with them the evidence of their ascent in the visible solid 
particles of dust, sand, and other light objects they whirl 
up with them in their upward course. 
The most marked difference between the dust storm 
and the waterspout or tornado lies in the essential differ- 
ence, as regards moisture, of the masses of air which are 
drawn into and ascend the columns of the whirlwinds. 
In the waterspout, certainly in all waterspouts that reach 
down to the surface of the earth, the earth is at, or not far 
from, the point of saturation, and in these cases the whirl- 
wind is accompanied with heavy rains. In some instances 
the rainfall has been so excessive that it can fittingly be 
described as only an aérial torrent of solid water, that 
from the velocity with which it falls from the clouds digs 
deep openings in the soil at the points where it strikes 
the ground. Thus immediately after the great tornado 
which occurred in Pennsylvania in June, 1838, Espy 
visited the spot and carefully examined the sides of the 
ridges and mountains on which its chief force was spent. 
He found many holes dug out by the torrents of water 
shot down by that tornado, which measured about thirty 
feet in diameter and from three to six feet deep, according 
to the nature of the soil and depth of the rock; the sides 
of the holes being in most cases cut down almost perpen- 
dicularly on their upper side, but entirely washed out on 
their lower side, so as to form the commencement ofja 
ravine. 
On the other hand, the air-currents which enter into 
and rise through the columns of the dust storm are very 
dry, and far removed from the point of saturation. Hence 
a large number of dust storms are neither accompanied 
nor followed by rain or any aqueous precipitation. Not 
a few, however, are observed to be followed towards the 
close of the storm with a sudden fall of rain, occasionally 
little more than a sprinkling, which may be due either to 
the condensation caused by the extreme rarefaction result- 
ing from the rapidity of movement of the gyrations of the 
ascending air-currents, or to the great height in the 
atmosphere to which the air-currents are carried by the 
storm. 
