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NATORE 
| May 14, 1914 
of the apparatus. The first description of this 
new departure was given in the Fortschritte auf 
dem Gebieie der Réntgenstrahlen for June, 1913, 
and more recently a further account has appeared 
in a later issue (Band xviii., p. 256). 
Dr. Lilienfeld creates an electric field in the 
neighbourhood of the antikathode between an 
aluminium tube and a white-hot wire. The work- 
ing potential difference is then applied to the main 
electrodes and a discharge immediately passes. 
Since the current taken by the tube depends upon 
the temperature of the so-called priming device, 
the operation is under control. 
But Mr. Coolidge? has simplified this design 
still further by placing a small spiral of tungsten 
at the centre of the kathode; heating this by an 
independent current he obtains a supply of elec- 
trons which are repelled and driven against the 
target with such speed as to produce copious 
X-rays where they strike. Thus, given a power- 
ful induction coil and noting that the bulb is so 
well exhausted that 100,000 volts at its electrodes 
produce no discharge, the spiral is heated and the 
current that then passes is simply a function of 
the temperature. Variation of the potential differ- 
ence would mean an alteration of the speed at 
which the electrons are driven against the target. 
The quality of the X-rays produced can therefore | 
be varied, irrespective of their quantity. This is 
not possible with any other type of X-ray tube. 
Its importance cannot be over-rated. It places 
in the hands of X-ray operators an instrument 
of precision. Many questions are still outstand- 
ing; it is not even claimed yet that this apparatus 
is beyond the experimental stage. Meanwhile, 
however, it may be of interest to point out that 
the Coolidge tube has already given some remark- 
able results. The most successful bulb so far 
made measured 18 cm. in diameter, and was 
blown from German glass; it carried a current 
of from 1°7 to 36 milliamperes with the spiral 
heated to a temperature varying between 2010° 
and 2240° absolute. It was run for fifty minutes 
continuously on one occasion with 25 milliamperes 
passing. There was, of course, great heat 
developed in the antikathode, but the regularity 
of the action seems to have been unaffected. No 
fluorescence appeared upon the glass of this bulb, 
and the starting and running voltages were identi- 
cal. The tube is also its own “rectifier,” and 
may be run off an alternating circuit without any 
additional device to suppress one phase. 
The prospect of being able to speed up the 
electron so much that it may give rise to a radia- 
tion with a wave-length equal to, or even shorter 
than, that of the Gamma ray from radium, offers 
great therapeutic possibilities. 
It remains so far to improve the means of 
supplying electricity to the tube that a steady 
potential difference may be maintained at its 
electrodes. Then, since reversal seems impossible 
with the Coolidge system, it should be feasible to 
produce pencils of approximately homogeneous 
1 A good summary is published in the Archives of the Réntgen Ray, for 
February, p. 340 
2 Physical Review, December, 1913. 
NO. 23224.) Vi0l 93) 
a Se 
X-rays in definitely measurable quantity and of 
a quality expressed in terms of the coefficient of 
absorption in some agreed substance. 
An attempt to construct a tube upon the new 
principle is at present being made in the physics 
laboratory of the Cancer Hospital, and experi- 
ments will be taken in hand there as soon as 
possible to test the types of ray obtainable by 
this means. Cuar.Les E. S. PHILLIPS. 
THE SICILIAN EARTHQUAKE OF MAY wa: 
| ape earthquake which visited the south-east 
flank of Etna on May 8 is evidently one of 
the strongest of the local shocks which occur so 
frequently within the bounds of the volcano. 
Unlike the Messina earthquake of 1908, the shock 
was heralded by many slight tremors in the sur- 
rounding district, several having been felt every 
day since April 25. But for these warnings, the 
loss of life might have been far greater than it 
was, though more than 150 persons are reported 
to have been killed and about 500 injured. The 
villages of Linera, Passapomo, Pennisi, and Zer- 
‘bati are completely ruined; Cosentini, S. Caterina, 
and S. Maria Vergina are half-destroyed; while 
about a dozen other villages from Zafferana and 
S. Venerina on the north to Trecastagni on the 
south are seriously damaged. 
The epicentre of the earthquake is clearly at 
and near Linera. The details at present known 
are insufficient to determine the boundary of the 
meizoseismal area, but its greatest dimension can 
scarcely exceed two or three miles. For the same 
reason, nothing more is known as to the extent 
of the disturbed area beyond the fact that it was 
small considering the violence of the shock near 
the epicentre. Probably the disturbed area is far 
less than that of some of the weakest of British 
shocks. This alone proves how rapid was the 
decline in intensity from the central region. At 
Acireale, only four miles south of Linera, the 
damage to property was slight. At Catania, 
seventeen miles to the south, the shock was felt, 
and excited some alarm. These two facts—the 
great intensity near the epicentre and the rapid 
decline in strength outwards—show that the focus 
_ must have been quite close to the surface. 
It is, however, in its relations with previous 
earthquakes in the same region and with the 
eruptions of the neighbouring volcano, that the 
interest of the earthquake chiefly lies. Two and 
a-half years before, on October 15, 1911, a simi- 
lar, though less destructive, earthquake occurred 
| in the immediate vicinity. The meizoseismal area 
in this case was a narrow band, four miles long 
and about a-third of a mile wide, extending from 
Fondo Macchia to Guardia, and passing about a 
mile and a-half to the north-east of Linera. On 
this occasion twelve persons were killed and forty- 
eight injured. On July 19, 1865, the same dis- 
trict was ruined by an earthquake, by which 
seventy-four persons were killed and _ fifty-six 
injured. Other shocks visited the same or 
neighbouring villages on July 11, 1805, and Janu- 
